With the clip selected in the Project Panel,
hit the 'Analyze' button (circled).
You will then get this pop-up:
Set your preferences, then hit OK.
Media Encoder will launch, and automatically begin the analysis.
Once it is finished, close Encoder, return to Premiere, and the
analyzed text will appear in the Metadata Panel (with that clip selected).
Speech Analysis isn't perfect... but it can give you a good start.