It is sort of hard. Joe has huge hands and fingers, but if you look closely at the picture in https://www.eaglesonlinecentral.com/...&postcount=766 I think you can tell that he is playing either an open "E" or and open "Am" (same fingering but different strings on those two chords). "E" is used a lot in rock music. In the country set, you'll see them playing a lot of "G" and "D" and "C" chords. Rock and Blues has a lot of Bm, E and Em and the 7th's chords.
In fact one of the most common "blues progressions" is "Em" then "B7" and then "A7". 12-bar blues....fun stuff!