Considering Catechism of the Catholic Church and its discussion on faith it states that "the certainty that the divine light gives is greater than that which the light of natural reason gives", followed by "Ten thousand difficulties do not make one doubt", how do we know when we are having difficulties and need to understand God better or have doubts? Faith seeks understanding, but at what point are we doubting?
157 Faith is certain. It is more certain than all human knowledge because it is founded on the very word of God who cannot lie. To be sure, revealed truths can seem obscure to human reason and experience, but "the certainty that the divine light gives is greater than that which the light of natural reason gives."31 "Ten thousand difficulties do not make one doubt."
The catechism is saying that faith is more certain than all human knowledge and asks the catechumen to continue in belief against all human knowledge to the contrary. The converse of this is when human knowledge seems to contradict what is believed through faith, thus creating difficulties for the believer. The more knowledge one has, the greater the possibility of possessing knowledge that appears to contradict faith. This is probably part of the reason that more highly educated people are likely to become atheists.
You will want to gain knowledge outside faith, in order to enjoy your life experience and to further your career options, but you will need to know that this can create difficulties. You will know when you face these difficulties when you learn something that puzzles you because it seems to contradict your religious beliefs. And you will know when you are doubting when you begin to feel that some contradictions can not be resolved, or you believe that some religious teachings need to be revisited by the Church.