The direct object marker ET is pointing to
Yehoshua יְהוֹשֻׁעַ or Yeshua יֵשׁוּעַ.
Here is the translation below.
✅️Zeḵaryah (Zechariah) 12:10 TS2009
[10] “And I shall pour on the house of Daviḏ and on the inhabitants of Yerushalayim a Ruach of favour and prayers. And they shall look upon [אֵת] Me [yeshua] whom they pierced, and they shall mourn for Him as one mourns for his only son. And they shall be in bitterness over Him as a bitterness over the first-born.
Zechariah 12:10
 - וְשָׁפַכְתִּי֩ עַל־בֵּ֨ית דָּוִ֜יד וְעַ֣ל יוֹשֵׁ֣ב יְרוּשָׁלִַ֗ם ר֤וּחַ חֵן֙ 
וְתַ֣חֲנוּנִ֔ים וְהִבִּ֥יטוּ אֵלַ֖י אֵ֣ת אֲשֶׁר־דָּקָ֑רוּ וְסָפְד֣וּ עָלָ֗יו 
כְּמִסְפֵּד֙ עַל־הַיָּחִ֔יד וְהָמֵ֥ר עָלָ֖יו כְּהָמֵ֥ר עַֽל־הַבְּכֽוֹר׃
ET is pointing to Yehoshua יְהוֹשֻׁעַ or Yeshua יֵשׁוּעַ.
אֵת# ET# את#