i haven't tried but i think their docker image or compose normally comes with bitcoin core built-in. so you would wanna manually create your docker compose and not include the core image. and instead you tell it to connect another node remotely using rpc. i think you can give host/user/pass via env or cli args.

not sure never tried.

since knots is a fork of core it should just work.

basically what you wanna search for is instead of running another node in the compose make it use already an existing node.

you don't have to specifically search for knots.

i think this is it: