وَمَآ أَدْرَىٰكَ مَا سِجِّينٌۭ
Sentence structure
The first interrogative مَآ is the topic and أَدْرَىٰكَ its predicate. The inner nominal question مَا سِجِّينٌ supplies what is made known.
Ayah summary
A person cannot know by themselves what Sijjin is.
وَمَآ — And what
Grammar: وَ resumes/coordinates; interrogative مَآ functions as the topic.
أَدْرَىٰكَ — can make you know
Grammar: A Form IV perfect with an understood subject; attached كَ is the first object and the following question supplies the second.
مَا — what
Grammar: An interrogative pronoun functioning as the topic of the inner nominal question.
سِجِّينٌۭ — (is) Sijjin
Grammar: A nominative noun functioning as the predicate of the inner interrogative مَا.