Can I delete all photos from my iPad only?

If you have enabled Photos in iCloud for your devices, iCloud synchronises your entire photo library between your devices; new photos are synchronised with all - as are photo deletions or edits.

If you disable Photos in iCloud, your devices each have photos stored locally. Deleting photos will delete the photo stored on your device.

If you do not want or require your photos to be synchronised between your devices, you simply need to disable Photos in iCloud:

Settings > [Your Name / AppleID] > iCloud > Photos > 

• iCloud Photos - set to OFF
• My Photo Stream - set to OFF
• Shared Albums - set to OFF

Additional information can be found here:

Set up and use iCloud Photos – Apple Support