How can I repair nail and screw holes if I don't know if wall is drywall or blueboard?
Asking the basic questions is what gets us started.... not silly at all.

If they are as simple as nail holes from picture hanging and the like, and there are only a few of them, use spackle. It comes in small quantities, pints for example, so much will not go to waste. It is intended for only small holes.

If there are a lot of repairs, you may want to go with joint compound, it is pretty much the same as spackle, it is easy to sand, water based for easy clean up, but you will get a bunch more for the about the same money. It is intended for larger repairs, or new drywall install, can be built up, but it does shrink a bit, not so that it will fall out. If the shrinkage is noticeable, add another coat, no biggie.

Plaster is way overkill for this type of repair, it requires a skill to use. I have tried to use it before years ago, and it set up as soon as it touched the wall, quite surprising. I now know were it is to be used nowadays, and nail repair is not one of them.