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This article will help you understand the general needs of gardenias: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/when-to-prune-a-gardenia.htm
The variety information on 'Jubilation' indicates they should be pruned in the spring.
To develop branching on the lower part of the plant, you're going to want to keep the top and sides trimmed, both to let more light into the lower areas, and to encourage branching on the lower branches. This article will give you a start in understanding pruning and shaping: http://pubs.ext.vt.edu/430/430-459/430-459.html

You can deadhead the flowers, but they do not need it. Simply pinch the blooms once they have died back at the base of the bloom, taking care not to disturb any new buds that may be forming.

I am assuming that you're inquiring about taking a cutting for a bouquet or centerpiece. If this is the case, then you can simply make an angled cut along the stem or branch with the flower attached and place this in water. If, on the other hand, you are wanting to take cuttings for propagation, then this article will help with that: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/propagating-gardenias.htm

Do the buds look or feel crusty? It is possible that your plant has thrips.They are hard to see and cause damage to the buds, making it diffiuclt for them to open. This article will help: https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm This article will help if you feel it is not thrips: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-flowers-gardenia-buds-falling-off-plant.htm Even if the buds are not technically falling off, the causes for bud/flower drop would also apply to buds not opening. Humidity can also be a factor. Either mist it every few days or place it on a pebble tray filled with water.

Epsom salt is magnesium sulphate. For gardenias, this will help prevent yellowing of the leaves but has nothing to do with blooming really. Give it some bone meal instead. That will add phosphorus. Gardenias that have too little phosphorus will look lush but will lack flowers. This article will give some other tips: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-care-to-get-a-gardenia-bush-to-bloom.htm

This article will help you: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/helping-a-gardenia-bush-with-yellow-leaves.htm