If you are asking if 'scoff' is an onomatopoeia, then the answer is a boring 'no'.
If it were an imitative sound, that is, 'scoff' attempting to sound like whatever mouth sounds you make when audibly displaying contempt, then the etymology of the word would say 'imitative'. For example:
oink (v. "to make a noise like a pig," 1965, of imitative origin.
As it is, 'scoff' has a much longer history.. It probably comes from Scandinavia, with cognates in Old High German. Eventually it started off with the PIE source *skeubh- "to shove".
The fact that it is borrowed immediately eliminates it from being considered imitative at the time of borrowing. (which is not to say that 'scoff' does evoke imaginatively some kind of pshaw or tsk or harumpf).
It is remotely possible that the PIEians (those who spoke PIE sitting around the campfire) shoved each other and the sound of this shoving sounded eerily like '*skeubh-'. And that may very well be considered imitative. But that doesn't make it imitative in English. For example, 'barbarian' is supposedly from Ancient Greek in their supposed imitation of non-Greek speakers babbling. It was imitative for the Greeks but not for English speakers.