Here, I've read through the famous Réti endgame study. However, there is a possibility that both sides can get a queen. For example, take a look at this variation.
[FEN "7K/8/k1P5/7p/8/8/8/8 w - - 0 1"] 1.Kg7 h4 2.Kf6 h3 3.Ke7 h2 4.c7 h1=Q 5.c8=Q+ *
I've consulted another Wikipedia page, entitled "Pawnless chess endgame", and it says "Queen versus queen: usually a draw, but the side to move first wins in 41.75% of the positions." You can also see the table from the "Tables" section, under the "Common pawnless endgames" subsection. It basically states the same thing. In queen vs. queen, the longest win is in 10 moves and the winning percentage is 42%.
I am really not very good at chess, but is the Wiki article totally correct? If it's correct, then, considering my 41.75 percent winning chance, how do I have to play in order to defeat my opponent if he/she and I both get a queen?