What is "dook dook" called in English?
Solution 1:
They are onomatopoeic words.
The definition of onomatopoeic reported by the NOAD is the following:
using or relating to onomatopoeia: onomatopoeic words like bang and coo.
Onomatopoeia is defined as "the formation of a word from a sound associated with what is named (e.g., cuckoo, sizzle)."
Solution 2:
I think the term you're looking for is Onomatopoeia, which means a word that represents a sound by sounding kinda like it. So for example, using "dook dook" to represent the sound a ferret makes, is done because the sound a ferret makes sounds like "dook dook".