can't open apple App Store OS Mojave

Please check:

Check the status of your network on Mac

Check the status of your network on Mac - Apple Support

If your Mac isn't connecting to the internet over Wi-Fi

If your Mac isn't connecting to the internet over Wi-Fi - Apple Support

If you can't connect to the App Store, iTunes Store, or other Apple services

If you can't connect to the App Store, iTunes Store, or other Apple services - Apple Support

-> If you tried all of the above steps and you still can’t connect, contact Apple Support.