In plain words
Among priests, Partha, know Me as Brihaspati, the foremost; among commanders I am Skanda; among bodies of water I am the ocean.
Word for word
And among priests know Me [as] the chief, Bṛhaspati, O son of Pṛthā; among commanders I [am] Skanda; among bodies of water I am the ocean.
The commentators
Bhagavadgītābhāṣyam· bhāṣya
पुरोधसां च राजपुरोहितानां च मुख्यं प्रधानं मां विद्धि हे पार्थ बृहस्पतिम् । स हि इन्द्रस्येति मुख्यः स्यात् पुरोधाः । सेनानीनां सेनापतीनाम् अहं स्कन्दः देवसेनापतिः । सरसां यानि देवखातानि सरांसि तेषां सरसां सागरः अस्मि भवामि ॥ २४ ॥
In plain words
And among priests, among the royal chaplains as well, know me to be their chief, their foremost — Bṛhaspati, O Pārtha; for it is precisely Indra's own priest who deserves to be called chief among all priests. Among army-commanders, among generals, I am Skanda, the very commander of the army of the gods. And among lakes — those pools said to have been dug by the gods themselves — among them, I am the ocean.
Close to the Sanskrit
And of priests, and of royal chaplains, know me, O Pārtha, to be the chief, the principal, Bṛhaspati. For he, being Indra's, would rightly be the chief priest. Of army-commanders, of generals, I am Skanda, the commander of the army of the gods. Of lakes — which lakes, dug by the gods — of those lakes, I am, I become, the ocean.