The meaning of «يلمزون» is to find fault, to taunt. Both «جهدهم» (with the dammah on the letter jeem) and «جهدهم» (with the fatha on the letter jeem) are valid recitations. That is, they give according to their ability by working and laboring.

Narrated Abu Musud: When we were ordered to give alms, we began to work as porters (to earn something we could give in charity). Abu Uqail came with one half of a Sa (special measure for food grains) and another person brought more than he did. So the hypocrites said, "Allah is not in need of the alms of this (i.e. 'Uqail); and this other person did not give alms but for showing off." Then Allah revealed:-- 'Those who criticize such of the Believers who give charity voluntarily and those who could not find to give in charity except what is available to them.' (9.79)