VSG_ALL = VSG_EINZEL + VSG_EINZEL_1 + VSG_EINZEL_12

import arcpy
# use workspace env or give an absolute path for fc
arcpy.env.workspace = "workspace"
fc = "feature_class"

# making a list of fields that contain VSG_EIZEL
# ex VSG_EINZEL, VSG_EIZEL_1, VSG_EIZEL_2
field_prefix = "VSG_EINZEL"
field_list = []
f_list = arcpy.ListFields(fc)
for f in f_list:
    if field_prefix in f.name:
        field_list.append(f.name)

# use update cursor to find values
# and update the total field
rows = arcpy.UpdateCursor(fc)
for row in rows:
    VSG_SUM = 0
    for f in field_list:
        VSG_SUM += row.getValue(f)
    row.VSG_ALL = VSG_SUM
    rows.updateRow(row)
    del VSG_SUM
del rows