I find the naming and compatibility of Yongnuo flashes quiet confusing. As far as i figured out a YN565 will work with TTL on a Nikon Camera, but not on a Canon. But will TTL work off camera with a master 568EX II on a Canon ?
I did not find a definitive answer, so i did what every reasonable person would do and just bought a used nikon and a canon version to test it :).
As slaves they both accept nikon and canon master TTL flashes, if set correctly.
Like Michael C pointed out, nikon flashes have a golden font on them, and canon is in silver.
Here I switched roles and accept nikon TTL signal by the canon flash and vise versa for demonstration purposes: So if I want to use both as TTL slaves I just set them both to C and use the YN568 EX II as master on a Canon body.
When working with a nikon body in this setup there are limitations obviously. You can take the nikon version to use TTL on camera, but the other flashes will only work in manual mode.
It depends on which version of the YN565 you have. There are both Canon and Nikon versions. Neither version is cross-compatible with the other system with regard to TTL on camera.
If you have the Canon version, TTL should work on camera or off camera with a Canon TTL Master flash, such as the YN568EX II.
If you have a Nikon version, TTL will work off camera with a Canon "Master" flash when the receiver in the flash is set to receive Canon optical TTL communications.
If the lettering on the flash is silver, it's a Canon version.
If the lettering on the flash is gold, it's a Nikon version.