That's not exactly analytical chemistry question

From what I know nitrogen oxychloride (NOCl) is oxidizing agent here. Cl^- are complexing Au³⁺ lowering potential of the Au oxidation.

HNO₃ + 3 HCl  --------->NOCl + Cl₂ + 2 H20
and
NOCl + Au ------------->?

In my opinion, it's just a matter of time. Aqua Regia should be prepared some minutes before you want it to react.
In the beginning:

3HCl + HNO3 -> 4H+ + 3Cl- + NO3-

...then, approximately after 15 minutes,...

4H+ + 3Cl- + NO3- -> Cl2 + NOCl + 2H2O

This is what I was taught to do for using aqua regia in order to dissolve HgS.

the 3rd reaction is when aqua regia has decomposed, so i dont think its needed in dissolving HgS because HgS is almost insoluble in water

Can you elaborate? I don't get it.

well i thought that the 3rd equation is the decomposition of aqua regia into its more stable products, and since water is formed as one of the products, that couldnt be used for dissolving HgS.

what i meant to say is that the last reaction was not needed for using aqua regia to dissolve HgS.

I infer you didn't understand what I meant. I was just trying to explain that aqua regia should be prepared just before adding it.
When you have to dissolve HgS, you simply need 'pure' aqua regia:

3HgS + 8 H+ + 12 Cl- + 2NO3- -> 3[HgCl4]2- + 3S + 2 NO + 4 H2O

Using heat to accelerate the whole process.

Of course you cannot use aqua regia, when Cl2 and NOCl (and water) substituted Cl- and NO3-, for such a reaction. So, in order to use aqua regia for analysing Hg, my professor told me to add HNO3 to HCl just before using it.
I just wanted to highlight the fact that acqua (in Italian that's the right spelling) regia can dissolve gold and HgS, if you pay attention to the same aspects.
I know very well you cannot dissolve HgS if there is water among the reagents.  

Hey I've got a further question: "dissolve" doesn't actually mean that a reaction takes place!
e.g. "ZnS is soluble in 2M HCl   ZnS + 2 HCl ------>ZnCl_2(aq) + H₂S_(g)"

Define "reaction".

That's an excellent question.

A (chemical) reaction is a phenomenon, which consists in some species (reagents) reacting for producing other species (products).

That's my opinion. So,

ZnS + 2 HCl ------>ZnCl2(aq) + H2S(g)

is a reaction (I'd call it a reaction of ionic exchange, whose physical consequence is ZnS's dissolution).

Technically speaking in a ZnS dissolution you are moving the reaction equilibrium to the right protonating S^2- anions. Le Chatelier's principle at work.