Will I be able to find out that someone is watching my hidden photos from another device on which my iCloud is?

Your questions is a little confusing but it appears you are trying to find out if someone can see your photos, such as hacking, and if you can see if they view them?

iPhones are virtually impossible to hack because of Apple's software. If someone is able to get into your device it would be due to them having your credentials (passwords and passcodes etc..)...

Can you clarify your questions and we'll be happy to assist.

Pingvinchik43 wrote:

I just don 't know English well . The question is different , I have iCloud that uses two iPhones . If someone goes to the hidden folder on another iPhone , will I find out about it .

Apple IDs should only be used by one person. If both of these phones are yours, make sure they have a passcode on them. If one of the phones is being used by someone else, have them create their own Apple ID.

No. If another device is logged into your iCloud account, the user can access anything in iCloud.