Hello,
do you know where I can find detailed instruction on how to import a BTG wallet (created with Copay) on Coinomi?
I have tried to insert the pass phrase (12 words), but the balance showed is 0 (probably due to BIP incompatibility).
I have also specified the derivation path (M/44H/0H/0H), but the balance is still null.
Thank you for the help!

You have to restore a wallet with the word seed in Coinomi from scratch, not sweep a wallet. Do not alter the derivation path when adding the btg part of your wallet. Only use the M/44H/0H/0H derivation path to get btg from btc that already were in your coinomi pre-split.