Learn Dash Documentation
1. Learn Dash Functions

a. Get user courses : learndash_user_get_enrolled_courses($user_id)
b. Get Lessons id by course id : learndash_course_get_steps_by_type($course_id, ‘sfwd-lessons’)
c. Get lesson list : learndash_get_lesson_list($course_id)
d. Get Topics list : learndash_get_topic_list($lesson_id, $course_id);
e. Check user access for course : ld_course_check_user_access($course_id, $user_id); //@returns true, false