There are 171 5-letter words containing J in the ENABLE dictionary — 2% of all 8,636 words at this length. J is worth 8 points in Scrabble and there is only one of it in the bag, which is why it tends to sit on a rack for several turns. A 5-letter word is usually the fastest way to make it pay rather than keep waiting for a longer one.
The J falls in the first position more often than any other, in 134 of them. 2 of them use the letter more than once — hajji, jujus, which is the case worth checking twice when a game has told you a letter is present but not how many times.
If you know more than one letter, this page stops being the fast way to find it. Enter what you have in the unscrambler — the Contains, Starts with and Ends with filters combine, and setting both length fields to 5 narrows this list to the handful your letters actually allow.