Hello. Have the same problem. I migrated from Multibit to Electrum, so I have no seed.
I`ve migrated by the wallet file.
That's not possible. Electrum does not read multibit wallet files. So, you either used a MultiBit
HD seed, or you must have exported your private keys from multibit, then imported those private keys into Electrum. Does your Electrum wallet say "[Standard]" or "[Imported]" at the top?
In any case, regardless of whether you used a BIP39 seed or imported private keys, you should still be able to see your private keys within Electrum... simply use the "Wallet -> Private Keys -> Export" option:
That will export
all the generated private keys...
if you just want the private key for a specific address, you can goto the "Addresses" tab (you might need to use "View -> Show Addresses" first), then right click on an address, and select "private key":