I don't understand (Surprise surprise!!). It says that the Dorian Mode sounds great over the ii chord. So in the key of G, if I play Am, do I play A Dorian or G Dorian, cause I don't really see the point of playing A Dorian.
A dorian. You have to look at it from a different perspective. Imagine it was an Am chord but not in the key of G.

A ii chord in a major key is a minor (seventh) chord (expandable, of course). So is the vi chord in a major key. For example: Am is not only the ii in G, but also the vi in C.

Normally if you played diatonically that'd be A aeolian (from C major), but if you did what you just said you'd play A dorian, the second mode of G major over it, because the ii and the vi chord are of the same quality.

Edit: my bad, switched up a few letters in my haste to go have dinner
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Me neither. He's not really making any sense. I don't know where he gets C dorian out of Amin7, but whatever.

Whoever said that means A dorian, but it's the same as G major.