Triple click at current cursor to select sentence

If by "sentence" you mean paragraph (defined by line breaks), then these standard macOS shortcuts should work.

To select the entire paragraph when the cursor is at any position in the paragraph, you can use these keystrokes:

  • -- make sure cursor is NOT at start of paragraph
  • ⌥↑ -- move to start of paragraph
  • ⇧⌥↓ -- select entire paragraph

Put each of those in a KM Type a Keystroke action.