Can you tell me in which part of world (country, city) is "mazar" of both Adam & Eve
and if they are allowed to visit this "mazars" by us.
Owing to the how long ago Adam and Eve passed away, the scholars have not been able to definitely identify where the final resting place of these figures is. One indication we do have is that the Prophet (peace and blessings of Allah be upon him) stated that prophets are usually buried where they resided. On that basis, the chances are that Adam was buried in and around the Middle East, possibly the Arab Peninsula. This is because we know Adam resided in Makka as he built the Kaabah there.
As for visiting Mazars of the pious, this is a proven practice of the Beloved Prophet (peace and blessings of Allah be upon him). We should perform Fatiha at such places where we pray for the transferral of reward to them (Isaal Sawab) and we should pray for ourselves there too, as they are places of significance and Barakah.