% ls -l DIR/mod/pending
and count lines with the owner execute bit set (rwx——–). Others are remnants from failed ezmlm-store runs (ignore - ezmlm-clean(1) will remove them).
There is currently no way to see this remotely, although you could easily install a script mailing the ls output in response to a message to e.g. ‘list-chkqueue@host’. For examples, see ezmlm-check(1) and How to add your own commands.