If you want to “print screen” or “take a screenshot” from your video inside Premiere Pro, maybe for a thumbnail, all you have to do is to click the camera icon (called “Export Frame”) in the Program window.

If you can’t find that button, click the plus sign in the bottom right corner of the Program window and then drag and drop that button onto your toolbar.
When clicking that button, you can pick a name and format for your image and then just click OK to save.
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I also have a bunch of short tutorials just like this one, in a playlist on my YouTube channel.
Thanks for reading, keep learning, and have a great day! ⭐️