Prefix trick tip
The tip about the prefix trick says, "Klingon also allows one to abbreviate sentences with -vaD if the recipient is first or second person (to me, to you, to us) and the object given a singular or plural noun, or an explicit third-person pronoun (him, her, it, them)."
This neglects the possibility of the prefix trick working with with no direct object being used. In fact, there is no restriction on what type of direct object, or lack thereof, may be used in conjunction with the prefix trick, so long as you can't mistake the prefix to be agreeing with a direct object. In describing the prefix trick, Marc Okrand uses the examples qajatlh I speak to you and tlhIngan Hol qajatlh I speak Klingon to you. qajatlh is unambiguously using the prefix trick, because the verb jatlh only takes speeches and languages as its object, not people. You can't jatlh a person, so qajatlh can only be employing the prefix trick.
So I would change this to something like this (maybe you can find a more elegant wording):
Klingon also allows one to abbreviate sentences with -vaD if the recipient is first- or second-person (to me, to you, to us). The verb must have a third-person direct object, or else it must have no direct object and not be able to take a first- or second-person direct object. An example of a verb that can't take a first- or second-person direct object is jatlh speak, which only takes things like languages and speeches as objects, so qajatlh I speak to you cannot be misinterpreted as meaning I speak you.
I've updated the tips and notes, and the changes should be visible at https://www.duolingo.com/skill/kl/Beneficiaries/tips-and-notes within a day or so.
(I've split up the example with jatlh into a separate paragraph further down, in case you're missing it when you look at the edited version later.)