One way of doing this is to:
1. Open the mixer by pressing either X, cmd-2 or the mixer button in the control bar.
2. Highlight the tracks you wish to route to a bus - if they're next to each other you can click/drag across them, if they're not, highlight the first one you wish to route then press cmd before clicking on the other tracks.
3. Where it says 'Output', approximately half way down the channel strip, click and hold. A small menu will appear. One of the headings is 'Bus'. When you hover the mouse pointer over the word 'Bus' a big list of buses will appear. Pick the one you want to route the tracks to and if that bus doesn't yet exist in the mixer, it will be created automatically.
4. Insert your Pro-Q on the bus and voila.
There are other ways to do this, including defining the routings from the Inspector visible down the left hand side of the main window or using the new 'track stacks' feature to create a 'Summing Stack', details of which can be found in the Logic X manual (search for 'submix').
Stan