You don't want to answer this word-placement question, now do you?

Prompted by this question I got to thinking about the placement of the word now.

If it's placed before the comma, it refers to an immediate condition:

You don't want to answer this word-placement question now, do you?

You might want to answer the question, but the situation is not urgent. You could answer it tomorrow. In fact, it might preferable to answer that question tomorrow if, say, it was your lawyer talking to you and your answer was going on the record.

But if you place it this way,

You don't want to answer this word-placement question, now do you?

it hasn't anything to do with time. Now functions in a different capacity, but I'm not really sure what that is. An interjection, perhaps? Something else?

The deictic temporal use of now is Semantic.

The meaning of the now of now do you? is not Semantic but Pragmatic. It's what's known as a Discourse Particle or Pragmatic Particle in the trade. It's called a Conversational Management Marker in this paper. (Very boring terminology, I agree. Science is like that; at least it's not in Latin.)

This particular now is often associated with (any combination of (images of)) a shaking finger gesture, a sneering facial expression, and a taunting intonation curve, together comprising a potential off-record face challenge, to put it in terms of politeness theory, one of the branches of pragmatics.

‘The Cambridge Guide to English Usage’ refers to words that ‘relate ideas to each other, helping to show the logic behind the information offered’ as conjuncts. Now, as used in the OP’s example, seems as if it might fit this description. The LSGSWE (‘Longman Student Grammar of Spoken and Written English’), however, goes rather further, and places such words under the overall heading of ‘Linking adverbials’:

The main function of linking adverbials is to clarify the connection between two units of discourse. Because they explicitly signal the link between passages of text, they are important devices for cohesion.

The LSGSWE identifies six major semantic categories of linking adverbial: enumeration and addition, summation, apposition, result/inference, contrast/concession and transition. Now is given under the category of transitional adverbials, but it seems as if the authors have in mind such use as ‘Now, that may be true, but . . .’ It’s more likely that the use of now in the OP’s example is as one of those linking adverbials that 'mark a concessive relationship: they show that the subsequent discourse expresses something contrary to the expectations raised by the precedingclause.' Now is not given as an example under that category, but it seems similar to one or two that are. In particular, it seems to perform much the same function as terminal though.

Now as used in the OP’s example is likely to occur only in speech, and, as such, its sense will be enhanced by prosody rather than by punctuation.

(For anyone unfamiliar with it, the LSGSWE is the stripped-down version of the magisterial ‘Longman Grammar of Spoken and Written English’.)