You need to build your own index, nostr isn't built for this, for this to work you would need to fetch all contact list (kind 3 events) an npub is mentioned in, then for each npub in those lists you'd need to fetch contact list events they are mentioned in.

Contact list events can be huge,like mb sizes huge, they might follow 1000s of npubs, so good luck,

Best way to do it would be to build your own index where you run this query once per user and then query your own index, managing updates would be another hassle though.