Do I owe Khums if I do not work continuously but rather work on and off throughout the year, mostly not working but sometimes taking small work here and there?
Khums is not obligatory on you if you have no savings at all after receiving your annual income and spending in your lawful usual expenses. If you have any savings no matter how much, then Khums is obligatory on that savings once per year. After paying the Khums from any amount, the remaining amount is called Mukhammas (Khums paid) and this Mukhammas amount is exempted from Khums in the coming years as far as it remains with you.
Wassalam.
Mohammad Al-Musawi