The 1988 Shunjusha edition of Dogen (ed. Kagamishima Genryu 鏡島元隆) gives this reading:
這箇はこれ誰そ誰かこれ我
kore wa kore ta so, tare ka kore ware
"Who is this? Who am I?" (or more provocatively "... is me?")
Points that might interest you:
這箇 can be pronounced "shako" but in most of the kanbun I've seen it's just assigned the reading "kore"
When 是 is used as a copula, as it is here, the "kore" is normally put just before the predicate, not at the start of the sentence: "X是Y" → "X (wa), kore Y" → (En.) "X is Y"
誰 is traditionally "ta(re)" in kanbun rather than "dare", because the rules for kanbun were set down before the first consonant of "tare" became voiced a couple of centuries ago