Answer 1

By searching :P

If you want help, you should provide a better description of your problem (what would you mean by "in it's row and column": in all matrix cells or only in each row and only in each column?) and a link to your own coding attempt ^^

Tips for starting:
In all cases, you could reduce the problem of finding repeated elements in a 2d list to finding repeated element in a 1d list... so start by writing such helper function ;)