Pt.1 Both are asking for a specific answer. Both can be used in choosing between two or among 2+ different things but "which" is used for this case more, I reckon. It really depends on how you use it. For example,
"Which is more appealing when encountering a difficult situation, to compromise or to perservere?"
"What do you do upon encountering a difficult situation, do you compromise or perservere?"
"Which one of those kids is your cousin?"
-no "what" equivalent
"What will I buy?"- asking for a specific answer
"Which will I buy?"-asking for sorvific answer but with a more narrowed down choice as the question could extend into something like "which one will I buy of these two dresses/ of all these desserts/ of the three wallets?"
Basically, which includes information whilst what may or may not include information.