Show him the way!
By extension: You are the one who must open his eyes, or create an opening for him. You need to help him and initiate a path for him to learn and understand ('את' sometimes means 'you' in the language of the Sages).
("And for the one who does not know how to ask – you open [the way] for him, as it is said: 'And you shall tell your son on that day'" – Passover Haggadah)
Translation
Expression (Hebrew)
אַתְּ פְּתַח לוֹ!
Definition (Hebrew)
בְּהַשְׁאָלָה: אַתָּה הוּא זֶה שֶׁצָּרִיךְ לִפְקֹחַ אֶת עֵינָיו, אוֹ לִפְתֹּחַ לוֹ פֶּתַח. אַתָּה צָרִיךְ לְסַיֵּעַ לוֹ וְלִיזֹם עֲבוּרוֹ דֶּרֶךְ לִלְמֹד וּלְהָבִין ('אַתְּ' לְעִתִּים מַשְׁמָע 'אַתָּה' בִּלְשׁוֹן חֲכָמִים).
("וְשֶׁאֵינוֹ יוֹדֵעַ לִשְׁאֹל-אֶת פְּתַח לוֹ, שֶׁנֶּאֱמַר: וְהִגַּדְתָּ לְבִנְךָ בַּיּוֹם הַהוּא" - הַגָּדָה שֶׁל פֶּסַח)