He (Brahma) is the head of all the demigods, and therefore he is addressed here (SB 3.15.4) as the head jewel of the demigods. It is not difficult for him to understand everything which is happening in both the spiritual and material worlds

Expressions researched:
"He is the head of all the demigods, and therefore he is addressed here as the head jewel of the demigods. It is not difficult for him to understand everything which is happening in both the spiritual and material worlds"

Srimad-Bhagavatam

SB Canto 3

Because Brahmā is almost on an equal footing with the Personality of Godhead, he is addressed here as the god of the demigods, and because he is the secondary creator of this universe, he is addressed as the sustainer of the universe. He is the head of all the demigods, and therefore he is addressed here as the head jewel of the demigods. It is not difficult for him to understand everything which is happening in both the spiritual and material worlds.

SB 3.15.4, Translation and Purport

O god of the demigods, sustainer of the universe, head jewel of all the demigods in other planets, you know the intentions of all living entities, in both the spiritual and material worlds.

Because Brahmā is almost on an equal footing with the Personality of Godhead, he is addressed here as the god of the demigods, and because he is the secondary creator of this universe, he is addressed as the sustainer of the universe. He is the head of all the demigods, and therefore he is addressed here as the head jewel of the demigods. It is not difficult for him to understand everything which is happening in both the spiritual and material worlds. He knows everyone's heart and everyone's intentions. Therefore he was requested to explain this incident. Why was the pregnancy of Diti causing such anxieties all over the universe?