If your cbq-engine process is not starting automatically after configuring your node to run the Query service and re-starting Couchbase using the OS service management, then please have a look in the query.log (in /opt/couchbase/var/lib/couchbase/logs) for clues as to why it isn’t starting, and post them here for us to assist with.
If you’re uncertain you’ve configured the Query service on a node, you could examine the output from:
curl -su Administrator:password http://localhost:8091/pools/default/nodeServices | jq
(the piping to jq is of course optional) (Ref: https://docs.couchbase.com/server/current/rest-api/rest-list-node-services.html)