The correct statement should be :
SELECT
student.firstname,
student.lastname,
exam.name,
exam.date,
grade.grade
FROM grade
INNER JOIN student
ON student.studentId = grade.fk_studentId
INNER JOIN exam
ON exam.examId = grade.fk_examId
ORDER BY exam.date
A table is refered to other on the basis of the foreign key relationship defined. You should refer the ids properly if you wish the data to show as queried. So you should refer the id's to the proper foreign keys in the table rather than just on the id which doesn't define a proper relation