Another (slightly crude) way is on your fields side bar for sourcetypes that have asset/identity fields (such as user) extracted, you should see the user_ fields with each user header (example: user_email, user_nick, user_first).
For assets I believe these are the src_ fields that match the asset header such as
src_should_update
src_is_expected
The easiest way to confirm that you have identities and assets being collected and presented correctly is with the following two searches.
|`identities`
and
|`assets`
If those commands produce complete & well formatted output, then it should be working.
I agree with nickhillscpl & it's one of the options listed in the doc:
https://docs.splunk.com/Documentation/ES/6.4.0/Admin/Verifyassetandidentitydata