Lang can fruit alone, but it still benefits from a partner. Most jujubes can fruit alone, but another cultivar often improves fruit set, size, and consistency. It flowers in mid bloom, which is worth knowing if you add a second tree later. Usually grown in USDA zones 6-10.
No single variety stands out as the obvious partner, but that is not a problem here: Chico, Li, So, Sugar Cane, and GA-866 all bloom close enough to work. There are 3 more in the list below. Pick whichever your nursery actually carries. Jujubes are best planted close enough for insects to work several trees in the same bloom window. In a home orchard, nearby spacing is usually easy.
To put that into practice: at a minimum, one self-fruitful jujube can work, but two cultivars are a better long-term plan. Better still, plant two or more jujube cultivars with overlapping bloom for stronger fruit set and better fruit quality. If you already planted one jujube, add a second cultivar before deciding that the species is shy-bearing in your climate.