Where? I mean is this a question for a specific spot? or I am missing something.

I personally don't have default 3bet-coldcall ranges. I cold4b or fold in most situations. Reason being that if you make a capped, tight 3betcoldcall range, it's gonna be fairly easy to play against and I don't wanna sacrifice the EV of cold4b-ing with AA,KK to strengthen this range, because I think it's not that + ev overall as a cold4b/fold strategy. Well.. this is only my opinion. If someone thinks otherwise I'd like to hear your thinking. :)
However, I do coldcall 3bets when I think it's the best decision exploitatively.

I think the best position to start experimenting with a calling range is BB vs SB/BTN. Their ranges will be fairly wide so you would be able to cold call a variety of hands so that your own range wouldn't be super transparent. However even in that spot I'm not sure how much EV you'd be gaining by having a cold calling range instead of a pure cold 4betting range and a pure cold4b range will be easier to play leading to fewer mistakes.

You are not explotable if you never coldcall. You have invested no chips before therefore a fold would always have EV of 0, so noone is gaining anything from you.

If you want to cold call, start with KK-AA.