Does the iPad 8th generation include the iOS 17.6 update?

Yes, the iPad 8th gen can be updated to the current iOS 17.6.1

Also see: Update your iPhone or iPad - Apple Support

Every time go to try to update it says update failed. Any reason why?

ashlyn1121 wrote:

Every time go to try to update it says update failed. Any reason why?

The following may have something that will help: If your iPhone or iPad won't update - Apple Support