he's got so little knowledge that he can't find a good job对吗

对的.
当n.前有many、much、few或little修饰词时,其前必须用so而不用such.
但要注意,这时Little表示少的意思
如果是小的意思,我们仍然用such,比如,such a little boy “如此小的小男孩”
so little water "如此少的水"