
As statements, the a. examples are awkward:
a. how powerful is the human will to learn.
b. how powerful the human will to learn is.
a. how intelligent is an animal.

b. how intelligent an animal is.
By the way, there this rule out there that warns us not to end a sentence with the verb
is - you'll find it along with other like rules, such as the one that states you shouldn't end a sentence with a preposition. Now, they aren't rules I follow, but some writers do follow them, and that in itself might account for the a. examples. The writer or speaker might invert the subject-verb in order to accommodate a rule - it makes no sense whatsoever, the rule as well as the resulting structure.
!End a sentence with
is. Otherwise ambiguity results:
b. how intelligent an animal is. <Word order tells us
an animal is the subject>
a. how intelligent is an animal. <Which one of those is the subject?>
The verb is copular. It links, conjoins, it's ambi-structural: X = Y and Y = X. The only way to determine the subject is to rely on the word order. The subject is always first.
X = Y <X = subject>
Y = X <Y = subject>
a.
how intelligent is an animal <not the subject of the verb>
b. how intelligent
an animal is <the subject of the verb>
All the best.
