I'm confused: Android does not use the removable SD card for app caches, and indeed I wouldn't know how to make it do that (except perhaps if you were rooted, or were using Marshmallow and had adopted the SD card). Some apps may default to storing data there (if present), in which case looking at those individual app's settings would be your best bet.
Are you sure you mean the actual removable SD card though (which the tablet may refer to as "external" SD)? There will also be something called "/sdcard", which is really part of the internal storage and actually will share space with the app/data space, which can cause confusion.
