How do I find cache on my iPad?

System storage includes a lot of cached data. iPadOS makes considerable use of available storage for temporary system caches.

Reported System Data can be expected to fluctuate. Your iPad will automatically and optimally manage its available system resources, using available free space to cache data and improve overall performance.

The only element of system storage that you can directly influence is your browser caches - which you can manually clear if you wish to do so.

For Safari:

Settings > Apps > Safari > Clear History & Website Data

Should you choose to do so, you can instead just clear cached website data without also deleting your browser history:

Settings > Apps > Safari > Advanced > Website Data > Remove All Website Data

For other browsers, you’ll need to find the relevant section of the App settings - which may be within the App itself.

Otherwise, transient system caches can be significantly reduced by performing a forced-restart of your iPad - although caches, by their nature, will again accumulate and be automatically managed by the operating system.

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Cached system data can also be cleared with a restore. More information about clearing system/other data is outlined here:

Clear Other storage on your iPhone or iPad - Apple Support

There no place you can universally clear cache on the iPad. You can clear it for Safari by following this: Clear your cache and cookies on iPad - Apple Support

It might be more useful if you would describe what you are actually trying to accomplish.

Cache files are part of System Data. Settings > Storage > System Data.

"clean up cache?"

You probably ought to start from the beginning and describe the reasons you need to do that. For example, if your iPad is not working as expected, try restarting it.

Restart your iPad - Apple Support