I have a Goodman GMNT080 furnace that I am attempting to place a humidifier on. The humidifier is a Honeywell HE260. I have a post to place the hot lead on the furnace, HUM (24v), where do I put the common as there does not appear to be any places left to connect the common?

You have to make one. You need to make a pigtail with the right connectors. Basically a "Y" connector with th eproper ends.

Usually the transformer has to be upgraded for the humidifier. If these are just the control terminals then you should be OK.