let me clear your doubt.
Yes you can give jam exam aftee completing your bsc. And here is the eligibility criteria for jam exam
A canditate after completing their bachelor degree are eligible for jam exam
A candidate belonging to general /obc (non creamy layer) should have atleast 55 percent aggregate marks ,without rounding off.
And those who belong to sc st should have at least 50 percent aggregate marks, without rounding off.
I hope my answer will help you out
Since the exam is on feb 2020, you can give the exam only when if you have completed your bachelors degree by that time because IIT JAM Eligibility Criteria mandates candidates to hold a Bachelor’s Degree . Candidates belonging to General/OBC (Non-Creamy Layer) category must have at least 55% aggregate in Bachelor’s. The marks secured include all the subjects studied at the graduation level, without rounding off the marks.