How can I restore the Clock app on my iPad?

Hello~ You can’t delete the clock app…so most likely you moved to another page or into a folder. Click on below and review…

Use Spotlight Search on your iPhone, iPad, or iPod touch - Apple Support

~Katana-San~

If you can’t find it searching for it as @Katana-San suggested, you probably deleted it completely on your iPad (which is possible in more recent versions of iPadOS.) in which case, download it from the App Store: App Store - Clock.