«وَمَا تَخْفَى خَافِيَةٌ عَلَى مَلِيكِكَ»
And no hidden matter remains hidden from your Lord.
Mā negates the present verb takhfā. The indefinite nominative khāfiyatun is the subject even though it follows the verb. ʿAlā malīkika completes the sense of what remains concealed and from whom.
An indefinite noun within this negative statement yields broad scope: no concealed matter escapes divine knowledge. Repetition of the root for hiding intensifies the point without altering the grammatical roles of verb and subject.