I'm presuming you mean JRT x Pug?
If so you need to be very careful to find a breeder who knows their stuff when it comes to conformation. Whilst crossing a Pug to a less brachycephalic breed is very likely to result in a better head, JRTs aren't always the best choice as some can have pretty iffy foreleg conformation. Shorter JRTs, which can be prone to having bowed legs, are not as appropriate a cross for a Pug as longer legged ones. Pugs have enough skeletal abnormalities without risking introducing new ones!! Underbites can be an issue in Pug crosses so this is also something the breeder needs to be aware of and be trying to avoid as much as possible.
Both breeds can be affected by Primary Lens Luxation so both parents should have either been DNA tested for it (with at least one testing clear) or be clear by parentage (with paperwork provided to prove this). Although there's no official scheme for it both should have had their knees thoroughly checked as both breeds can be prone to Luxating Patella. The Pug parent should also have been DNA tested clear (or be clear by parentage) of May-Hegglin Anomaly. The JRT parent should have a current eye test done via the BVA Eye Scheme. The Pug should have been screened for Hemivertebrae as if their vertebrae are extremely deformed then a first cross may not necessarily result in pups with normal spines.
That's the absolute minimum I'd be looking for. Ideally they should be doing all available DNA tests for both breeds so they know exactly what, if anything, the pups they're producing might be carriers for. You can see the lists of currently available tests here: Pug and JRT. It's those conditions with the specific breeds listed which are the ones a conscientious breeder would be utilising.
A Pug x JRT is potentially going to be a much more active and game little dog than a pure Pug. You may also have to contend with higher prey drive and possible lower tolerance of other dogs (the latter doesn't mean aggression, this is a good explanation of dog tolerance levels which is applicable to many terrier breeds). If you're not comfortable with having what is essentially a terrier then a cross where you could potentially be getting just that probably isn't a great idea.
Pug x terrier can be a really nice little cross and some breeders in Germany have used a terrier outcross to reduce exaggeration in Pugs with great success but it does need to be done carefully, with proper consideration given to health, temperament and conformation.