1) Will it require to produce the evidences at the time of filing the divorce on the ground of mental and physical harrasement??
marriage photo + certificate or other documents from which it can be inferred that the marriage is solmnized is sufficient to get the case admitted. other evidence TO PROVE UR ALLEGATIONS will be required at evidence stage.
2) As you know such harassment only happens in the 4 walls of matrimonial house, so its too much difficult for me to produce the evidence at later stage also., so what should I do to prove those harrasments in court?
depending upon the facts of your case, u need to adduce evidences in support of ur allegations. Mere allegations without any proof are not sufficient. Oral evidence should be also supported with documentary one so as to make it trustworthy.
3) What other evidences should I collect which may help me later??
depends upon the facts of ur case - eg. medical treatment docs. after u were physically abused, witnesses (if any) ...
4) If I can't produce the evidences then will I not get the divorce?? So what will happend in that case?? How long the court give the decision???
in lieu of evidences, ur petition will not succeed.