How can I punish the "bad" knight on c3? I play the Caro–Kann Defence against 1.e4 as black, and for whatever reason it feels like I get the following line way too frequently:
[FEN &quot;&quot;]

1.e4 c6 2.d4 d5 3. exd5 cxd5 4. Nc3?!

This line is a &quot;non-critical&quot; line, so much so that I just got an opening book on the Caro-Kann and there are a whopping 0 lines that discuss how to play against this setup. It's very rarely played in the masters databases, but on lichess.org it's the 4th most common move in this position, and you can also reach the same position by playing 1.e4 c6 2.Nc3 d5 3.exd5?! cxd5 4.d4 which isn't too uncommon.
Similar to the c3 knight in the Richter–Veresov Attack or the &quot;Jobava&quot; London, mostly I just see people dismissing this knight, claiming off-hand that it's bad, that it &quot;doesn't belong there&quot;. But for whatever reason, when I look at my results in the different lines in the Exchange Variation, this is my worst line! I'm probably running into problems with a small sample size, but I'm wondering if anyone has any general tips for how to make white feel this &quot;bad knight&quot;.
I'm wondering if anyone has any general tips for how to make white
feel this &quot;bad knight&quot;

The fact that you manage to put &quot;bad&quot; and &quot;bad knight&quot; in scare quotes shows that there is some hope for you. White does not have a bad position. I suspect that this line isn't played much at master level because it isn't the best way to squeeze every last scintilla of advantage out of white's starting advantage of having the first move.
But there is no universe in which you can look at white's position and seriously think that white has a bad position which black must punish. If you think like that as black then you are on the way to losing.
Four moves into the game and white has already -

Staked a claim to the center with a pawn on d4 (black matches this with a pawn on d5)
Developed a piece to a good central square, the knight on c3 (black is behind but it is black's turn so can remedy this on the next move)
Has free development for both bishops (black has free development for only one bishop)

White is not worse. Black is not better. Has black completely equalized? It doesn't look like it.
So, your best approach is to accept that white's first move advantage may have decreased slightly but your job remains the same during the opening - try and equalize via good development. How you develop your pieces will depend to a certain extent on how white develops. Pay attention to all the things you normally do during the opening and aim to reach an even middlegame where you can try and outplay your opponent.
At all costs avoid trying to punish your opponent. This will only lead to bad moves and an early loss.