Catalysis of the reaction: L-lysyl36-[histone H3] + 2 S-adenosyl-L-methionine = 2 H+ + N6,N6-dimethyl-L-lysyl36-[histone H3] + 2 S-adenosyl-L-homocysteine. This reaction is the successive addition of two methyl groups to the lysine residue at position 36 of histone H3, producing histone H3K36me2.