Is there a command to list SVN conflicts?

Just use grep!

svn st | grep '^C'

If you have already merged you can use

svn status

and see an uppercase "C" for conflict, but usually you shouldn't see such kind in your working copy.

You could try svn merge -r <revision> --dry-run and see what happens that way.

On Linux, if you want to see only the conflicts, pipe the status through grep.

svn status | grep -P '^(?=.{0,6}C)'