
what about- about which thing or matter
um welche Sache/Angelegenheit
which ... about- about this thing or matter (which is being spoken of)
um diese Sache/Angelegenheit (von dem/der gesprochen wird)
around what- around which object
um welchen Gegenstand (herum)
around which- around this (just mentioned) object
um diesen (eben angesprochenen) Gegenstand (herum)