If I haven finished playing BGII: SoA can I play BGII: ToB?
It is completely possible to start BGII: ToB without having finished BGII: SoA. There are two parts to BGII: ToB: an Add-in section and an Add-on section. The Add-in section is new content added into the BGII: SoA, whereas the add-on content continues the story after the events of Shadows of Amn. The Add-in section is the dungeon of Watcher’s Keep, which is larger than Durlag’s Tower from Baldur’s Gate: Tales of the Sword Coast, and one of the coolest areas ever created for any Baldur’s Gate game! Watcher’s Keep will show up on both the BGII: SoA and the BGII: ToB maps. This means that you can play the dungeon while continuing Shadows of Amn (you will also have the option of playing Watcher’s Keep dungeon from the Add-on section). If you wish to play the Add-on section without finishing BGII: SoA, the game will proceed as if you had finished Shadows of Amn and you won’t be able to return to the Shadows of Amn areas.