You can get the universal replacement, European car type coolant at most auto parts stores; it is fairly pricey so get the full strength concentrated gallon jug and not the prediluted jug, and that way you will have enough to dilute down and refill your entire system...ask the store clerk to look up car and show you what is compatible, then read the bottle labels carefully. It is pretty common to lose coolant on a Q7 via the EGR Cooler going out (mine did recently), as well as more typical clamp leaks, hose leaks, water pump seal, etc., so don't take it for granted there's no problem and topping off is all it needs...there's likely an underlying cause to why it's low, since it's a sealed, pressurized system.

Audi uses the term "lifetime fluid fill" because it sounds good, but it's just a marketing gambit aimed at new car buyers. While they do use very high quality, extended-life, and fully synthetic fluids throughout the car, which provide for a longer service interval between changing fluids, none of these fluids are "lifetime" rated by the fluid mfgr's and certainly not by the component's manufacturer (transmissions, diffs, xfer case). If you do a little research, you'll find you should be changing all of the fluids on your Q7 on a regular interval schedule, just like any other vehicle you intend to keep running long-term, most especially the fluids Audi lists as a 'lifetime fill', such as in the tranny, differentials, transfer case, etc., which are some of the highest cost components to replace.