I am not familiar with the term "pop up" rose and the internet isn't helping. If you want, repost with the formal name of the rose or what is on the plant tag. Roses are pruned in spring in NJ and most other places. You know it is pruning time when the leaf buds on the canes are swelling or just starting to open. This often coincides with forsythia blooming. Pruning stimulates new growth which is not the signal you want to send to the plant now. New growth will be tender and killed by winter. Fertilizing is saved for spring. Nitrogen moves through the soil and will largely be gone if you fertilize now. Fertilizer also sends the wrong message: your plant needs to harden off and prepare for winter. Cutting back to 6 inches isn't necessary. For now, just prune out dead, diseased and damaged canes. The following link goes to a list of articles on rose care including winterizing. https://www.gardeningknowhow.com/search?q=rose%20care
