Bhashya
किंदेवतः का देवता अस्य तव दिग्भूतस्य ।असौ हियाज्ञवल्क्यः हृदयमात्मानं दिक्षु पञ्चधा विभक्तं दिगात्मभू-तम् , तद्द्वारेण सर्वं जगत् आत्मत्वेनोपगम्य, अहमस्मि दि-गात्मेति व्यवस्थितः, पूर्वाभिमुखः— सप्रतिष्ठावचनात् ;यथा याज्ञवल्क्यस्य प्रतिज्ञा तथैव पृच्छति— किंदेवतस्त्व-ह्येव रूपाणि प्रतिष्ठितानि ; हृदयेन हि स्मरणं भवति रूपा-णां वासनात्मनाम् ; तस्मात् हृदये रूपाणि प्रतिष्ठितानीत्य-र्थः ।एवमेवैतद्याज्ञवल्क्य ॥
In plain words
'What god' really means: what god belongs to you, now that you've become the directions themselves? Because Yajnavalkya has taken his own heart, split it five ways across the compass, and made it his very self — through that he has swallowed the whole world into himself, standing there facing east, thinking, I am the self of the directions. So Shakalya questions him on his own terms, all the way down to forms resting nowhere but the heart. Because it's the heart that remembers a form — and a form is nothing but a trace laid down in memory. So forms rest in the heart. Just so, Yajnavalkya.
Close to the Sanskrit
'What deity' means: what deity does this direction-become entity, [namely] you, have? For this Yājñavalkya has made the heart his very self, divided fivefold among the directions, become the self of the directions; through that he has taken the whole world as his self, and stands established thinking 'I am the self of the directions', facing east — as the word 'sapratiṣṭhāḥ' implies. Just as was Yājñavalkya's own profession, so accordingly he [Śākalya] questions — 'what deity...' down to 'forms alone are founded'; for it is by the heart that memory of forms, which are of the nature of latent impressions, occurs; therefore the meaning is that forms are founded in the heart. 'Just so it is, Yājñavalkya.'