Methyltransferase which catalyzes the formation of N(2)-methylguanosine at position 6 in a broad range of tRNA substrates containing the characteristic 3′-CCA terminus of mature tRNAs (PubMed:34669960). Also catalyzes the formation of N(2)-methylguanosine at position 7 of tRNA(Trp) (PubMed:34669960). Requires the methyltransferase adapter protein TRM112 for tRNA methyltransferase activity (PubMed:34669960).