To find out the extent to which it exists in your riflescope, do the following: With your rifle solidly supported on sandbags and while looking through the scope at a distant target, move your head back and forth in the scope's field of view. If parallax is present, you'll see the crosshairs move across the face of the target, even though the rifle is immobile. If the scope is parallax free at that distance, there will be no apparent movement. Repeat this test at several distances that represent the most common ranges you face when hunting.
Riflescopes designed for long-range shooting almost always feature a parallax adjustment, even though beyond about 500 yards optical physics dictates it's really not required. For my money, the place where parallax adjustment is most sorely needed in average hunting rifles is in rimfire scopes. This is because those same laws of physics dictate that at close ranges the parallax effect is most pronounced. Those short ranges are why you won't see a serious competitive rimfire rifle or a competition airgun without a parallax adjustable scope, and it's why I much prefer to have a scope like that on my hunting rimfires.
Unfortunately, rimfire scopes with parallax adjustment are somewhat rare, especially in a size and configuration suitable for hunting. During the last year I've been using one that meets all my qualifications and which I can recommend to anyone looking for a good rimfire scope. It's the Nikon Prostaff Target EFR. There's that "target" word again, but just ignore it; this is a great hunting scope. EFR stands for Extended Focal Range, a fancy way of saying this scope can be set parallax free anywhere between 10 yards and infinity.
This is a 3-9X44mm scope with a 1-inch tube that features a fairly typical dual-X type crosshair. However, Nikon has added a small dot at the junction of the fine crosshairs (image below), and I find it works great on the small critters we normally engage with rimfires. Windage and elevation knobs are finger adjustable with positive clicks and can both be reset to zero, making dialing hold-offs a practical technique for longer shots. There's also a quick-focus eyepiece and, of course, it's nitrogen sealed to keep it fog-proof.
With a price well under $200, this is a great rimfire or airgun scope for a hunting rifle. Rimfire season is coming and now's the time to get geared up. If you're thinking of a new scope, give this one a serious look.
P.S. Did you know North American Hunter has an online store?