According to Wiktionary , "hujambo" is short for "huna jambo", which means "Do you have anything?", and "sijambo" is short for "sina jambo", which means "I don't have anything". What is "hawajambo" short for? And are "huna", "sina", (and the form with "hawa") verbs?  https://en.wiktionary.org/wiki/hujambo
By comparison, hawajambo would be short for Hawana jambo. The words sina, huna, hawana are all negative forms to "have" which is taught later in the course.
Nina - I have Sina - I do not have Una - you have Huna -you do not have Wana- they have Hawana- they do not have
The question mark at the end.
In spoken Swahili, the intonation is different. It can be similar to the questioning intonation in English, or it can also be a lot stronger, with the last two syllables having a distinct sound, almost like an English question where the speaker is just holding back from shouting the last syllable.