Pencil Tool    P

Sets the current tool (left-click) to the Pencil Tool. Correctly entered the command is ‘T’ then ‘P’. The ‘T’ command pops up the tool menu, the ‘P’ command selects the Pencil Tool.

Common Logic Pro tools — Apple Support

Use the Pencil tool to add new regions or events. You can also select, drag, loop, and alter the length of regions or events using the Pencil tool. In the Score Editor, you can use the Pencil tool to add dynamic markings, accents, and other symbols to notes.