I don't think you can set a weapon model on player spawn ._.
Try this
PHP Code:
register_event("CurWeapon","CurWeapon","be","1=1")
PHP Code:
public CurWeapon(id)
{
new Weapon = read_data(2)
if( Weapon != CSW_KNIFE )
return PLUGIN_CONTINUE
new vModel[20]
format(vModel,19,"models/noj12.mdl")
entity_set_string(id, EV_SZ_viewmodel, vModel)
return PLUGIN_HANDLED
}