Giving donation to online darul iftaa websites

The general principle in regard to Sadaqah-e-Jaariyah is that Sadaqah-e-Jaariyah will be obtained by spending wealth, time, energy, resources, etc. in any valid permissible cause which will benefit the creation e.g. Building a well, Musjid, Madrasah, teaching Deen, etc. As long as people benefit from that cause the donor will continue receiving reward.

And Allah Ta'ala (الله تعالى) knows best.