The meaning of the word assumed

Assume does not itself connote falseness or pretense, although it may be used alongside other terms which do: assume a disguise, for instance.

In the present case it might bear either or both of your other senses: practitioners may assume (=undertake) the duty of reporting child abuse to the authorities because they feel their personal and professional ethics requires them to do so, or they may (rightly or wrongly) assume (=take it for granted) that the law requires them to do so.

Nothing in the structure or grammar tells you. If the context fails to make it clear, then either the writer has failed to make their meaning clear or you are missing knowledge the intended audience is expected to have.

In context, assumed duties means “presumed duties”, “duties supposed without proof”. Presumed would have been a better word to use. As your question points out, assumed creates confusion. Readers might misunderstand assumed duties to mean “accepted duties”.

Taken as a whole, the text is calling attention to mistaken presumptions about the legal duties of guidance counselors. The next sentence refers to these same duties as “apparent” (that is, supposed without proof) and goes on to say that practitioners’ real duties are different than what they might presume. Thus context makes the meaning clear.

I agree with the accepted answer, but I think this is a case of very bad writing. The writer seems to be trying to say that the patients assume the practitioner has a duty that they may not actually have.

But that is very much not the standard use of the phrase "assumed duties." To assume, when the object is a duty or privilege, normally means "to take on along with something else."

• When you become a king/queen, you "assume the throne." The throne is something you get along with being king.
• When you become president, you "assume the duties of the presidency." The duties of the presidency are something you get by becoming presidency.
• When you buy a property with an unpaid lien, you "assume the debt." Because you got that property, you now have to pay the debt.

It seems like this writer had the phrase "assumed duties" bouncing around in their head and then misapplied it to refer to someone's inaccurate presumption about someone else's duties.