How to Know Whether Manas Is Engaged in Exertion, Investigation, and Deliberation?

How can one know that the manas is diligently engaged in investigation and contemplation? When you feel that there is always a critical phrase or a doubt lingering in your mind, it signifies that the manas is contemplating and investigating. When your mental attention is consistently focused on the critical phrase, and your mind is perpetually filled with questioning—even without overt analytical thinking—yet those doubts and thoughts remain persistently present, unable to be shaken off, this precisely indicates that the manas is engaged in profound investigation.