Fair use is always a fact-driven issue, and the details matter. That said, copying a single ad in order to criticism the ad, or comment on it, is very likely to be found to be fair use. If only a section of the ad were shown, to illuminate the point being made, that would make a fair use holding more likely. Or if the entire ad was shown in low resolution's for context, and a detail shown in higher resolution, that would also help.
Such an ad is largely factual, not creative in the way that a work of fiction or fine art is, which leans toward fair use. Such a reproduction of the ad will not serve as a replacement, nor harm the market for the ad, which leans toward fair use. The use seems to be transformative, which leans significantly toward fair use. If the whole ad is shown that leans somewhat against fair use, but that does not prevent the use being held to be fair use.
As for trademark protection, that is not likely to be an issue. Trademarks are protected against being used in trade (also known as "in commerce") without permission. This means using the mark to label, identify, or advertise a product or service of the same general type as the product the mark is properly associated with. Using the mark, or a similar mark, in such a way that people are likely to be confused into thinking that a product or service came from the same source as the mark, or approved, endorsed or sponsored by the mark owner, is usually infringement. Using the mark to discuss the product or service, and in particular using it as the name of the product or service, is nominative use. Nominative use is not infringement. Using an ad that includes trademarks to discuss the associated product is a form of nominative use.