All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The ruling on earning by watching advertisements differs depending on the on the different advertisements themselves, and as long as it promotes something permissible, there is nothing wrong with profiting from watching it. If the advertisement is for a permissible commodity but contains a religious impediment, and it can be avoided, such lowering the gaze to forbidden images or turning off the sound of music, then there is no objection to watching it as well as making money from it.
As for advertisements that promote something forbidden, such as wine, pork and usury, then it absolutely impermissible to profit from watching it.
Allah knows best.