Is there some generally accepted notation for squarefree, cubefree, etc. numbers?
And is there also some notation for squareful, cubeful, etc. numbers?
I don't think there is any generally accepted notation for those numbers. But you could of course define those sets, for example the cubefree numbers
$$\Bbb Z_{c.f.} = \{a \in \Bbb Z \mid \not\exists b \in \Bbb Z \setminus \{1,-1\} \text{ s.t. } b^3 \mid a \}$$
or else.