Is there anyway to know if your private key is being used in multiple wallets/platforms?
For example, if I have your priv key and imported that into my wallet, will you be able to know about it? unless I make a transaction of course.
No, i believe you won't. Since i could have your private key in an offline wallet aswell, until i sign a message or make a rawtransaction with it, you should/could not know if it is compromised or not.
Some desktop/web wallets might automatically make contact with a node, but that still shouldn't reveal you using private key X, as far as im aware. ( Unless you sign a transaction ofcourse.)
Although i never heard about the wallets automatically contacting nodes unless the transactions happens but of course if some wallets are automatically contacting the node that doesn't mean it will be revealed to the owning person.