Jajja is the thirteenth letter of the Gurmukhi painti and the third member of the palatal series, the voiced unaspirated j. It completes, with Chachcha and Chhachha, the part of the palatal group whose sounds a modern Punjabi reader hears exactly as they are written, since the two letters that follow behave differently in living speech. The three way distinction the series makes at the palate, voiceless plain, voiceless aspirated and voiced, is the same distinction the velars make further back in the mouth, and the repetition of that pattern across all five series is the organising idea of the whole alphabet. Jajja is a frequent letter in Punjabi and in the language of the Guru Granth Sahib, standing at the head of a substantial family of words concerned with birth, living creatures and the world.
In the extended set outside the painti, a dot written beneath Jajja gives the z of Persian, Arabic and English borrowings, a sound the language did not natively hold; that dotted letter is a later addition and not one of the thirty-five. The dotted extension is a good example of how the script has grown without being redesigned. Rather than adding new shapes, Gurmukhi took an existing letter with a related sound and marked it, so the extended set is legible to anyone who knows the painti and costs a reader nothing to learn. That approach has limits, since it depends on there being a near neighbour to borrow, and it is why the six extensions cluster among the fricatives and sibilants rather than being spread evenly across the alphabet.