On PC you can find your Might and Magic X Legacy save game files in the following directory:
C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegames\[Account ID]\401 (Uplay PC)
C:\Program Files (x86)\Ubisoft\Ubisoft Game Launcher\savegames\[UID]\403 (Steam)
If you are having issues with the Cloud Save feature in Uplay, you can manually copy the above folder and place it in another computer's Uplay install directory to continue your save from the first PC.
On Mac you can find your save files in the following default directory: