From #wikidata a few minutes ago:
[11:31:48 PM] <nichtich> Hi! I am looking for a way to query the list of enables site prefixes. https://www.wikidata.org/w/api.php?action=sitematrix shows ALL Wikimedia sites, also those not enables for Wikidata. AFAIK it's wikipedia, wikivoyage and commons, but how do I query only those and how do I make the query also return other Wikimedia projects when these enable Wikidata?
[11:32:38 PM] <legoktm> if you're looking for the easy way https://noc.wikimedia.org/conf/wikidataclient.dblist is what you want
[11:32:46 PM] <legoktm> the *proper* way would look like...
[11:33:38 PM] <legoktm> nichtich: https://www.wikidata.org/w/api.php?action=paraminfo&modules=wbgetentities&format=jsonfm
[11:33:57 PM] <legoktm> under parameters, name: 'sites', look at the 'type' key
[11:34:03 PM] <legoktm> a bit weird
[11:34:22 PM] <legoktm> there probably should be a proper API module for this
action=query&list=wikibaseclients or something.