CAT Eligibility

Yes, Diploma students can appear for these exams.

Refer to the link given below-
https://www.shiksha.com/college/jbims-jamnalal-bajaj-institute-of-management-studies-churchgate-mumbai-344/admission.

Aggregate marks till that semester can be considered.

Yes, proper preparation with proper strategy will make you crack the exam. You can achieve whatever you want just make a proper way to get it. First of all, go through the syllabus of CAT 2020 then start preparing for only those topics
https://www.shiksha.com/mba/articles/cat-2020-exam-blogId-25095.

You can apply in the last year of your degree.

Hi. Kindly visit the link. https://www.shiksha.com/mba/cat-exam-registration.

You can go through the link given below-
https://www.shiksha.com/college/indian-institute-of-management-Tiruchirappalli-Chennai-campus-ekkatuthangal-49131/admission.

After clearing your supplement exam, one can be eligible for CAT