The container that your Wax Plant (Hoya carnosa 'Compacta')
is growing in appears quite large for the size of the plant and the soil looks extremely wet. Hoya's require pots with really good drainage and a porous soil. I'd suggest removing the attached saucer from the pot, which can hinder air circulation. The black spots on the leaves may be a fungal issue due to the soil retaining too much water and lack of proper aeration at root level.
Fungus Gnats are usually present when soil stays too wet.
Spider Mites are usually present in dry, arid conditions with lack of air movement.
If you repot your plant, I'd suggest using a small pot that has lots of drainage holes in the bottom and use a potting medium like the one Rose suggested. I've been using a mixture of potting soil combined with lots of perlite and orchid bark mix that was recommended to me about 15 years ago by an experienced Hoya grower.
Hoya Compacta has very pretty, fragrant blooms but I no longer grow it because it was a mealybug magnet in the humid climate here in Florida where I live and it was extremely difficult to eradicate the mealybugs from all those nooks and crannies.