Return score in reference UI

in Query Tester, documents will show the document score. How can I get this information back into reference UI?

You'd probably need to download the Reference UI and customize the code yourself. This might help you get started if you want to do that: Reference UI - how to modify what's displayed (React newbie) - #2 by JasonStoltz

If you just want to know for some one-off requests what the score is, you can look at the API response body in your browser's network tab for the "http://localhost:3002/api/as/v1/engines/pokemon/search.json" request. Specifically, in the results field, each result has a _meta.score property.