As far as i have heard,this career fair has been established to provide employment opportunities to qatari nationals,BUT, since you are a Doha resident,i would advise you to attend the career fair because you will have nothing to lose,and besides the vast number of companies and corporations that are taking part in the fair is sure to interest any job-seeker,whether Qatari or non-Qatari,so go for it,and INSHA ALLAH all the best!