please can someone tell me which one is correct (Thesis's title vs Thesis' title). Or if both options can be used?
Depending on the style used, it's currently more common to add an 's to any singular noun that ends in s. That would make it thesis's. (This is what what The Chicago Manual of Style prefers—with a few seldom-encountered exceptions). But it used to be that only a ' would be added, and it's not uncommon to still find that system being used. (Whichever system you use, make sure you are consistent.)
You can avoid the question by rephrasing it to title of the thesis.
However, there is actually no need to use the possessive at all in this particular case—and most people would actually find it odd. You can use thesis title as a non-possessive noun in the same way that we use door knob rather than door's knob.