To get a single instrument into the Last Score command you write the expression:
(compile-score 'score-title :instrument 'instrument-name)
After the evaluation you can see the part using cmd-alt-ctrl-N command, this key shortcut will display the notation of the chosen instrument.
This is the tenor part from the 'Origami Letters' score (Lesson 3) found in the Quick Start workspace.
(compile-score 'Origami-Letters :instrument 'tenor)