وَمَا تَخْفَى خَافِيَةٌ عَلَى مَلِيكِكَ
And no hidden matter is hidden from your true Sovereign.
Mā is negative; takhfā is an imperfect verb; and khāfiyatun is its nominative subject. ʿAlā malīkika is a prepositional phrase attached to the verb.
The negative construction with an indefinite subject gives the denial wide scope: no secret falls outside that knowledge. The cognate wording takhfā / khāfiyah adds emphasis.