People don't really see the differences between both of (شغل ، عمل ) and it's not really clear .. but
عمل used as - job ,work , do or make .. -
شغل - what you are busy with, what fill your time, do or work -
That in فصحى
In the other accents
Palestinian /Jordanian / Syrian / Egyptian
عمل - make, do -
شغل - work in something , job -