In the sentence
 He is the most talented artist (that) I know
what is (that) I know in terms of function – an indirect complement, licensed by most, or simply a common postmodifier? Why?
Similarly, what is in the world in
 the most talented artist in the world
Addition to the original post: Having read the answer and the comments that I've received for this question, along with answers to other questions about licensing and the modifier/complement distinction, I have to give this another go:
According to the comments below, we are dealing with modifiers rather than (indirect) complements in both the above examples. Now, I'm not doubting the validity of these comments – I just still don't understand. This is why:
As far as I've been able to understand, licensing is all about setting up "slots" for specific kinds of structure. For instance, a verb such as give sets up a slot for something being given, and a slot for a recipient; consequently it licenses two object complements (direct and indirect object). Part of the deal is also that the slots set up are specific to a subset of "licensers"; in this case: not all verbs license two objects.
Now, to me it seems that this 'setting up slots that are specific to a certain subgroup' is exactly what superlatives do, something that, I think, is supported by John Lawler's answer below:
Most is a superlative marker and takes a superlative construction. One of the things required for the construction is a range for comparison
Looking again at  and , it seems to me that both the relative clause in  and the PP in  elaborate on the "range-for-comparison-slot" set up by most; hence, they should both be licensed by most, no?
Now, if these dependents are indeed licensed, they should be complements – shouldn't they? Only, since they aren't licensed by the head noun, but rather by another constituent within the NP, they'd be indirect complements.
This is my take on all this – could someone please explain to me where I go wrong, and how I should think instead?