diploma students are eligible for this exam
Mention the name of the exam for which you want to know. After completing diploma if you want to pursue engineering you can appear for lateral entry examinations , you can also appear in JEE mains. But you cannot get admission through jee mains. After clearing mains you can appear for JEE advance and if you can get a good rank in JEE advanced you can get into IITs.
I hope this helps.