The transom one is (I assume?) used to help drain water out of the cockpit after righting the boat after capsize (boat is not self-bailing so this won't drain all water though) maybe after beaching the boat to bail? I'm basing this on how my 1979 DS II is set up, since my old Widgeon was a 1969 and had the wooden seats.
The one on the forward bulkhead must have been added by a previous owner to drain water out of the forward section of the boat (stowage area under foredeck) I assume your boat is a 1971-82 model that has a forward deck? If newer, and she has an area in the bow level with the side seats, then the plug is to drain the forward locker/cooler.
There should be one more drainplug in the outside of the transom to drain the inside of the boat (bilge between deck and hull).