Thanks for the upload.
Your site may benefit from a persistent object cache.
Your slowest queries come from a plugin that seems to be called Tutor LMS Pro. Your core WordPress queries seem to be performing well.
Here’s your slowest query, which took about 1.54 seconds.
SELECT DISTINCT quiz_attempts.*, quiz.post_title, users.user_email, users.user_login, users.display_name
FROM fgt_tutor_quiz_attempts quiz_attempts
INNER JOIN fgt_posts quiz ON quiz_attempts.quiz_id = quiz.ID
INNER JOIN fgt_users AS users ON quiz_attempts.user_id = users.ID
INNER JOIN fgt_posts AS course ON course.ID = quiz_attempts.course_id
INNER JOIN fgt_tutor_quiz_attempt_answers AS ans ON quiz_attempts.attempt_id = ans.quiz_attempt_id
WHERE quiz_attempts.attempt_ended_at IS NOT NULL
AND ( users.user_email="" OR users.display_name LIKE '%%' OR quiz.post_title LIKE '%%' OR course.post_title LIKE '%%' )
AND quiz_attempts.attempt_ended_at IS NOT NULL
ORDER BY quiz_attempts.attempt_ended_at DESC
LIMIT 20 OFFSET 0
I’m not familiar with that plugin, but it does appear that this particular query is not designed for efficiency. Your best path to improving this is through the plugin developer.