estimating what it might see is fairly easy, to calculate the best possible resolution an optic can achieve in the visual spectral range you just divide the diameter of the primary mirror or lens in cm by 11.6 and that gives you the dawes limit resolution in arcseconds.
jwst is infrared so multiply whatever number you get using that formula by about 2 to get a good estimate of jwst's potential if the optics are diffraction limited.
https://www.youtube.com/watch?v=UI6pSkIs_tc 
