Short story, I have this private key, but not sure at what crypto currency it belongs (surely not BTC/LTC) and I was wondering if there was a way to check if the private key belongs to a specific coin automatically without trying for each crypto (I saw that I can do it via GUARDA wallet, but it will take days). An additional point would be to get also the balance in it, if 0, makes no sense to proceed further.
Private keys are tied to particular wallet and not on particular cryptocurrencies!
Also, if you have your private keys and you don't have the wallet address then the private keys remains useless so also when you have your wallet but looses your private keys.
Meanwhile... You can actually track wallets historical transactions and also what cryptocurrency and account balance it holds but can not have private access to it.
So with the certain information provided, you would literally not be able to know what coin in the wallet and the value of the coin.