What sensor can I use to determine rotation?

https://duckduckgo.com/?t=ffab&q=HOW+DO+SENSOR+GLOVES+WORK&atb=v101-1&ia=images&iax=images&iai=https%3A%2F%2Fpub.mdpi-res.com%2Fsensors%2Fsensors-23-06693%2Farticle_deploy%2Fhtml%2Fimages%2Fsensors-23-06693-g003.png%3F1690373659

There is  a lot of information about this on the web. 

MK

accelorometer, inclinometer, gyroscopes can all do this. 
depending on how you do joint articulation you may be able to use a magnomometer, or encoder.
then you can also make your own sensors with that packing foam, and conductive thread. 
you could read the capacitance changes, or... 
well there is a lot of things you could do, without further detail on constriction, it s hard to say. 
is it joint position in 3d space?

** WUT WUT?!? ** 
>> Gang signs detected!

good idea but why not flex sensor ,its more good if i want it to directly touch to skin ,it wont even give a scratch or cut on skin

There are always multiple ways to approach a solution. Give flex sensor a test and let us know result. Which flex sensor are you considering ? 

I was thinking a micro absolute encoder , but there would need to be an rigid exo-skeketon. The sensor accuracy wearing gloves or other attachment would have inherent slippage. 

Solid state sensors like magnetometers, imu, gyros involve alot of calibration,  calculation,  and proper filtering, which why I only use them when they are the best solution. 

ok, i will use the sensor as u suggest so which is most perfect sensor in this case

I recall that there are some sensor glove based student projects listed here:

https://people.ece.cornell.edu/land/courses/ece4760/FinalProjects/ 

I have one of these Essential Reality P5 gloves. This video from LGR provides some insight into what kind of performance you might achieve....

https://www.youtube.com/watch?v=wOSmrpw89SI

Another commercial example...

QD023 Motion-Sensing Glove for Robot Control – ACEBOTT

Aniket_kumar_raj said:

I thaught of potentiometer but its too large to fit between finger joints

Perhaps take a look at some of the small SMD ones ?

Bourns do some thin rotary position sensors:
https://www.bourns.com/data/global/pdfs/3382.pdf

flex sensors are a thing, they are prone to mechanical failure. 
you can make them, for pennies, which is what I was trying to suggest.
IDK, I cant find the videos of mine right now. 
well, if you're going to choose the method prone to mechanical breakage, dont go with 5$ sensors.