On the periodic table, no officially named element begins with the letter J. The modern table contains 118 named elements, and their English names use every letter of the alphabet except J.
This is a fact about English element names, not chemical symbols. Some symbols come from Latin or other historical names, and symbols do not always share the first letter of the English name. For example, sodium is Na from natrium and potassium is K from kalium.
Temporary systematic names for newly identified elements can differ from permanent names, but the officially approved English names still contain no element beginning with J. “Jodium” is an old or alternate spelling associated with iodine in some languages, not an official English element name.