$ ssh remote-host "epmd -names"
epmd: up and running on port 4369 with data:
name some_node at port 58769
Note the running on port for epmd itself and the port of the node you're interested in debugging. Reconnect to the remote host with these ports forwarded:
$ ssh -L 4369:localhost:4369 -L 58769:localhost:58769 remote-host
On your machine, start a hidden Erlang node running the observer app:
$ erl -name debug@127.0.0.1 -setcookie if-server-has-one -hidden -run observer
N.B.: If the server is using -sname, you need to use -sname as well, because Erlang™. You'll also need to change your system's hostname to match the target host, for the same reason.
In observer, go to Nodes - Connect Node and type some_node@127.0.0.1.
You can also get a remote shell:
$ erl -name debug@127.0.0.1 -setcookie if-server-has-one -remsh some_node@127.0.0.1