he, alright.
Not sure how many tries we get now, so I still go with three tries
Let's analyse the situation:
We know that the Knocker knocks and we also know that he knocks in the mine to lure miners to gas chambers. So spot three is obvious, too obvious if youcatch my drift.
We also know that the Knocker is crafty, would he thus go for such a completely obvious ploy? I think it makes for more sense for him to knock behind the wall with the super rare material to prevent us from getting it
And yes, I am aware that this is a "He knows that we know that he knows" situation. But we have one more advantage: Yulia is wearing a mask, if there is gas behind spot number three she should be fine.
Now on to spot four, not much we can seemingly infer from that one, except that it has a crack. A crack could mean there is pressure behind it. Also the number four happens to mean Death in japanese. Could be a complete coincidence, buuut, still.
I don't expect any danger behind the unmarked spots, so if we want to play it safe we could probably just go for them, but that's boring.
My vote is...6 2 3 in that order. Since Yulia has her mask we should let her do the digging. Goma and Cherchiel should stay near the exit to make sure a swift retreat is possible in case of a cave in or gas leak. Oh and Goma might sound the horn, just to make things easier on Yulia