What BIP32 derivation path does Electrum use for Multisig? Same question as What BIP32 derivation path does Electrum use? 

but for multisig. thanks.
Electrum uses BIP45.

m / purpose' / cosigner_index / change / address_index

Example for non-change of the first cosigner and first address: m / 45' / 0 / 0 / 0

See: https://bitcointalk.org/index.php?topic=1634517.15
and
https://github.com/bitcoin/bips/blob/master/bip-0045.mediawiki