I’m assuming you are using JSON for DQL mutation.
How to “connect nodes” is explained at
https://dgraph.io/docs/mutations/json-mutation-format/
you can totally send a mutation that will create two nodes that are “connected”.
Note that “connected” in Dgraph just means that an entity has a predicate to a uid (an other entity).
Happy to help if you have a sample of what you want to add in graph using DQL mutation…