If you are going to use Sen2Cor from SNAP using the Sen2Cor plugin, then the plugin can install it for you. When the plugin is installed in SNAP, in Menu → Tools → Manage External Tools, edit sen2cor and install it from the Bundled Binaries tab:
S2?_MSIL1C*.SAFE but is XXXXXX.zip Error
Sen2Cor does not support the zip format, so if you want to apply it to a S2 product, you have to unzip the product before opening it in SNAP.
AttributeError: 'L2A_Tables' Object has no attribute '_L2A_Tile_PVI_File'