The name valley of Hinnom does not occur in the Targum Isaiah 66:24 which I happen to have.
Targum Isaiah 66:24 And they shall go forth, and look upon the carcases of the men, the sinners, who have rebelled against my Word : for their souls shall not die, and their fire shall not be quenched; and the wicked shall be judged in hell, till the righteous shall say concerning them, we have seen enough.
Targum Isaiah wasn't written in English. The word 'hell' there is translating 'Gehenna'.
You can see the original text of Targum Jonathan here: http://cal1.cn.huc.edu/showtargum.php?bookname=12&chapter=66&verse=24&Peshitta=&Sam=
'Ge-Hinnom' is the seventh to last word in the sentence (from the left): גֵיהִנָם
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