How can I tell if someone logged in to my macOS Sierra? It seems as though the activity in my Console has been deleted. Is this possible? There is no data before the login that led me here tonight.
Yes, ever since macOS Sierra, it is possible that Console isn't displaying your past activity. You may want to refer to this question: Sierra Console.app show earlier data

With regard to your question title, it's not clear exactly what details you're after, but one option open to you is using the last command in Terminal.

More specifically:


Launch Terminal (usually found in the Utilities folder)
Once the square cursor appears, type last
Press the enter key


This will produce a list of sessions in reverse time order.