O alias da tabela de associação do modelo Laravel adiciona automaticamente o prefixo da tabela
Opção um:
$result = DB::table("user_exams as ue")
->leftJoin("exams as e","ue.exams_id","e.exam_id")
->leftJoin('users as u',"ue.user_id","u.user_id")
->select([
"ue.user_exams_id",
"e.exam_title",
"u.user_name",
"ue.check_status",
"ue.pay_status",
])
->where($params['where_callBack']??[])
->paginate($pageSize);
Opção 2 (versão necessária):
$result = (new UserExams())->setTable('ues')
->from("user_exams as ues")
->leftJoin("exams as e","ue.exams_id","e.exam_id")
->leftJoin('users as u',"ue.user_id","u.user_id")
->select([
"ue.user_exams_id",
"e.exam_title",
"u.user_name",
"ue.check_status",
"ue.pay_status",
])
->where($params['where_callBack']??[])
->paginate($pageSize);