Sostituisci store
come di seguito:
public function store(Request $request)
{
$this->validate($request, [
'job' => 'required',
'machine' => 'required'
]);
$spkAdmin = new SpkAdmin();
//On left field name in DB and on right field name in Form/view
$spkAdmin->user_job = $request->input('job');
$spkAdmin->machine = $request->input('machine');
$spkAdmin->save();
}