How can one examine their level of tawhid and by extension their level of shirk/nifaq? Any book recommendations as well upon this matter. May Allah (سبحانه وتعالى) bless you ustadh and guide you to everything He loves and may He make you among those He loves the most.

Ustadh AbdulAziz al-Haqqan

Evaluate yourself through your obedience and disobedience to Allah (subhanahu wa ta'ala). Look at how you are when you are alone, and how you are in regards to the commands and prohibitions of Allah and His Messenger (sallallahu alayhi wa sallam).