There isn't much to see here from the outside. The building is locked unless you contact the Jewish community ahead of time to open it or go on a synagogue tour. But I still think it's worth coming by this site simply because it's important.
This is labeled in Arabic on Google maps, or it's simply the spot marked with a Star of David and labeled "Synagogue" southeast of the Haret Zuweila churches. It's directly south of El Adawy Primary School which you can find on Google maps. It is not, however, at the location marked "Maimonides Synagogue" on Google maps. That's in completely the wrong section of al-Qahira and there's nothing there (I went there myself to make sure).
There were many synagogues in this area before the 1960s when nearly all Egyptian Jews left. We walked by several old sites. Some are completely gone, some have been converted into mosques, and some are just ruined. I think I found the Talmud Torah synagogue which was converted into a mosque, just north of Darb al Homosani and across from Abd El Mageed Abd El Gawad restaurant. And we walked by what should be the Haim Capussi Synagogue on Nasir Alley. I didn't read the graffiti so if there is something nasty in the photo, I'm sorry.
I will definitely go back to do a lot more exploring, and maybe to see if we can talk to someone who has lived in the neighborhood for a long time.