As far as I understand, "what questions has this will to truth not laid before us!" seems to be a question; but I don't know why it does not end with question mark.
Would you help me to get the reason, please?
This looks like a question, but it is not intended as one. It's intended as an exclamation. Really, it's a rhetorical question, used only to draw attention to the questions that have been 'laid before us'. Strictly speaking, it should have a question mark, but the author has chosen the exclamation mark to emphasize that it's intended as an exclamation.
This looks like a question, but it is not intended as one. It's intended as an exclamation. Think of it as the exclamation "What questions this will . . . has . . . laid before us!", but with an unusual, literary word order.
You could also think of it as a rhetorical question, used only to draw attention to the questions that have been 'laid before us'. If you think of it in that way then, strictly speaking, it should have a question mark, but the author has chosen the exclamation mark to emphasize that it's intended as an exclamation.
The word 'what' can be used as a determiner to introduce an opinion, usually in an exclamatory sentence. You can see this function more clearly in the sentence that follows the one you are asking about. Normally you would not see subject-verb inversion with this use of 'what', so the author has indeed expressed the sentence as a question. However, the sentence expresses an exclamatory rhetorical question, rather than a "real" question.
What speed you have, Clive! I didn't see your post before I posted.
I am fine. Thank you. Haven't seen you for ages. How are you?
It's getting cold in Canada, isn't it, Clive?
Yes, today it is around zero degrees.
Today it's around 8 degrees. A little warmer than usual for this time of year here.
It's been warmer than usual around here, too. It's a sunny 54° F (12° C) in my neck of the woods today.
"Neck of the woods" -- I just had another interesting expression.