Where can I find the rpc api endpoints for electrum? Somehow I cannot find a list of the possible rpc commands. Basically they are just the bitcoin rpc commands I guess but I cannot find a list for that either...

There are some examples here:
http://docs.electrum.org/en/latest/merchant.html#jsonrpc-interface

Also there is a list here but e.g. addrequest from the link above is not in there:
https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list
Electrum RPC methods a little different from full bitcoin node RPC. You can run help command in order to get all methods. Here is an example:

"addrequest",
"addtransaction",
"broadcast",
"clearrequests",
"commands",
"create",
"createmultisig",
"createnewaddress",
"decrypt",
"deserialize",
"dumpprivkeys",
"encrypt",
"freeze",
"getaddressbalance",
"getaddresshistory",
"getaddressunspent",
"getalias",
"getbalance",
"getconfig",
"getfeerate",
"getmasterprivate",
"getmerkle",
"getmpk",
"getprivatekeys",
"getpubkeys",
"getrequest",
"getseed",
"getservers",
"gettransaction",
"getunusedaddress",
"help",
"history",
"importprivkey",
"is_synchronized",
"ismine",
"listaddresses",
"listcontacts",
"listrequests",
"listunspent",
"make_seed",
"notify",
"password",
"payto",
"paytomany",
"restore",
"rmrequest",
"searchcontacts",
"serialize",
"setconfig",
"setlabel",
"signmessage",
"signrequest",
"signtransaction",
"sweep",
"unfreeze",
"validateaddress",
"verifymessage",
"version"