Landwert 35 is going to be his address at the time the weapon was issued to him. Correct, Biessenhofen or Biessendorf (you used two spellings) would be the town/city and I believe Amriswil is the Canton (state). Hop over to the Swissicon Rifle Forum and check these threads out

K31 ID Tags

Letter to the one on the Tag. in General Discussion Forum

Tag abbreviations military ID-numbers. in General Discussion Forum