These are some practical tools I've used in my own life to determine if someone is an N or S. I had many of these people take the mbti test afterwards to check my accuracy. This is quite accurate, although not being a T, I didn't bother to find out the exact accuracy :p I just cared that it works lol
The Quick Test:
When you meet someone new, ask them how their week went. When they are done talking, ask them specific details about it. Note whether they are excited to share SENSING details such as who was wearing what, colors, sights, sounds, who said what, who did what, etc. Then, when you are done, turn the topic to something abstract. I go to Christian groups so I often mention some truth in the Bible or something about life. A question is best. Note their excitement and willingness to talk about the subject, as well as any obvious introspection that they must have done on their own time.
Note: Sensing types can talk about intuitive topics and Intuitives can talk about sensing topics, but the willingness and ease of which they talk about each is the key to finding out whether they are an S or N. Take into account any education they may have on the subject, as this can help Ss talk with more ease about N topics. You must also factor in Ns who grew up around many sensors, or young Ns who have not fully developed their Intuition, who will tend to talk about sensing topics much more frequently.
1-2 Hour Test:
If you have a chance to sit down for an hour or two and have a discussion with the person you are most likely gonna figure out by the end whether they are S or N. I have yet to meet an S that can talk about abstract concepts for that length of time. They can do it for about 30 mins or so, but they WILL get frustrated and bored if it continues on past that. You WILL even likely scare them off :p My N friends and I have literally talked for 4-5 hours straight about purely abstract concepts and ideas, and enjoyed every minute of it. And then called each other up later that week for another long talk :p Ns want to analyze, analyze, analyze. Watch for that, it's a key sign.
On the other hand, S's can talk for hours on end about the latest movies, trends, music, etc. and not get bored. Note: Ns can talk about things they are interested in for hours, but S's will talk about what is HAPPENING, whether it is their particular interest or not. Try talking like this for more than a few mins to an N and they will try profusely to change the subject to something they consider "meaningful", which doesn't have to be something deep with all Ns, just something conceptual or analytical :p If that doesn't work they will suddenly remember they had to run an errand and excuse themselves from the conversation.
How to spot an NF and an NT:
During your long talks, an NF is going to want to analyze feelings. They will tend towards playing the role of psychologist. They will get into why someone is feeling what they are feeling and HOW that person can be helped or encouraged. Abstract concepts are important only as related to people and they will quickly bring the conversation back to the goal: helping people and often helping them emotionally or attending to their emotions. If they really like you and trust you, they will share of THEMSELVES with you. To an NF that means their dreams, fears, values, feelings, hopes. This is a HIGH honor, don't take it lightly. It is how NFs bond and if they are sharing these things with you, that is exactly what they are trying to do, form a deep bond with you.
NTs care just as deeply about people and the world, but are not as good at interpreting their own emotions or the emotions of others. Because they do care, they are likely to want to "solve the problem" itself and use their understanding of concepts to help them do that. Making someone feel good emotionally does not solve the problem in their eyes. They actually want to HELP people, not just make them feel good. If you share with them a problem at work, they are likely to find the flaw in the system of administration, not a better attitude that you could have to deal with the situation (which is what an NF would tell you). During your long discussions with them they will talk about systems and not always bring it back to the people involved. They enjoy talking about how things work, or don't work properly, and how they can be improved.
Both types enjoy analyzing, analyzing, analyzing and can have some awesome discussions and learn a lot from each other. The NF helps the NT be more aware of emotional problems, so they can factor that into their plans to better the world. And the NT makes the NF aware of the faulty systems at work so that they can see past their emotions to a better long-term solution.
SJs and SPs:
This is a bit trickier for me, since I'm an NF myslef :p Still, it can be done. Best way to tell an SJ from an SP is not to talk with them, but to WATCH them. SJs and SPs are the busy bees. They don't sit down for very long lol
SJs will likely be taking care of someone or meeting some need. They will do this in a structured way, even on their time off. They are the people at the meeting who come in and set up early, making sure everything runs smoothly. Things running smoothly is key here. They care about everything being done in a presentable, acceptable way with every issue and person being taken care of and all needs attended to. Their world feels out of control when something is left undone, or someone is left unhelped
SPs are more carefree. They will be busy but in a different way. They want to be in on the action. They'll be the ones test driving the set-up that the SJs put together. Taking care of people in a structured way is not as important to them. You will see them interacting with people, helping in their own way, but a bit of chaos is exciting to them and they will not rush in to solve the problem. If they are more introverted they won't necessarily see it as exciting, but they will NOT feel it is their personal responsibility to make sure things run smoothly and will likely keep to themselves.
Hope this info is helpful to you. In my own life I've used these methods to quickly spot compatible types. I now have several VERY CLOSE NF friends that I can connect with on a deep and meaningful level. The kind of friends I've wanted my whole life but didn't know how to meet or where to find them. I've also been able to connect with all the different types in a meaningful way that they appreciate. Which means my likeability has gone up LOL and I am making many friends. It's great to be able to quickly tell someone's type, speak their language and get to know them. It makes for a great first impression and opportunity to have many good friendships.