Even though we call it an autosomal test, 23andMe also tests SNPs on the X and Y chromosomes, as well as mtDNA. You can see the SNPs that were derived in its Haplogroup Mapper under Ancestry Tools. The defining (most recent) SNP is listed first.

They use an obsolete alphanumeric nomenclature. In fact, this type of nomenclature is obsolete. FTDNA and most genetic genealogists use the format (major haplogroup)-(defining mutation). Your brother would then be R-L48. You can then go to the ISOGG site and look up the defining mutation to get the current alphanumeric notation, if desired. Note that some SNPs have more than one name.

http://www.isogg.org/tree/