Hello,

If you are in engineering diploma final year then you are eligible to appear in JEE main exam as those who are in their final year of engineering diploma are eligible to appear for the exam, but you can't get admission in any NITs, CFTIs or IIITs because Diploma holders are not eligible to take admission there, you can only go for JEE advanced  only if you qualify JEE mains, and only after qualifying JEE advanced, you can get admission in any of the IIT.

Hope this helps, all the best.