adding H to a molecule

[Elyssa Smith 4B]

When something asks for the conjugate acid of a molecule like CH3NH2, how do you know where to add the hydrogen to (can you explain general terms)?

Also, if you are adding to a molecule like C6H5O-, how would you know to add the H to the O and not to the existing H's? (this makes C6H5OH and NOT C6H6O)

[Hiba Alnajjar_2C]

During discussion, my TA pointed out that drawing the Lewis structure of the molecule can help you determine where an H could logically be attached. For this example, you would draw out C6H5O-'s structure and identify that the O atom is the best place to attach another H.