Need help finding the best continuation.


You probably should have thought about how to respond before you played d5, not now.
However, SakoC is correct. You can take the pawn with the knight. However, your knight is currently en prise. Therefore the following continuation is possible:
9. ... Nxd4 10. Bxd4 Nxd5
Of course, you can interpose a check first with
9. ... Nxd4 10. Bxd4 Re8+ 11. Be2 Nxd5
However, you need to be careful because of this continuation:
9. ... Nxd4 10. Qxd4 and now you have a small problem because the pawn on d5 has two protectors (ignoring the pinned knight on c3). It looks like you might have just lost a pawn and that 8. ... d5 was a rash move.
The tactics here are too hard for a player at your level. Black can play nxp, but after white plays nxn attacking the queen, white is up a knight for a pawn and threatening the black queen, so black needs to be able to see that Qh5 check will recover the piece.
There is a more advanced tactical play here that I dont think I would see in a game. Na5 is actually the best move, because it gets the black knight out of the way with tempo (by attacking the bishop). The pawn on d5 is still taken after the bishop moves to d3 (or after exchanging the knight for it on b3) and white has some significant continuing problems thereafter.