The search function of Standard Site Search uses javascript for real-time results. As a result, Google Analytics cannot measure the search actions by default. The search actions first need to be sent to Google as an event. More information about this method can be found in this article: https://support.tweakwise.com/nl/cat/starter/165

After the method above has been implemented, you can find your visitors' search actions on the tab Events of Google Analytics. Click  Behavior > Events > Top events.

Go to Event category > Search.

Choose Search and then request.complete. Here you can find an overview of all active search terms: