Hello mariano95,
Does the device you're using (from the screenshot) have a passcode/password lock on it? If so, try entering that in the box.
If that hasn't helped you may try entering in the passcode that may be used with other devices, if you have any others.
If all else fails, you may try selecting the 'Don't know Password?' option from the screenshot. This may prompt to reset iCloud encrypted data. This page has a chart on which data is end-to-end encrypted, which varies if you're using standard or advanced data protection: iCloud data security overview
Cheers.