I would definitely place the opening capitals passage indicator after the opening question mark for the following reason: Although not explicitly stated in the UEB section on capitalized passages, UEB 8.3.3 states "Only a modifier or a ligature indicator can be positioned between a letter and its capitals prefix." By extension, I believe the capitals passage indicator must occur after the opening question mark and before the first capitalized letter: ⠢⠠⠠⠠⠙⠬⠝⠙⠑⠀
I don't think there is a hard and fast rule about the terminator. UEB 8.6.2 says that "the capitals terminator may precede or follow punctuation and other terminators but it is best that indicators and paired characters ... be nested". The example in UEB 8.5.5 shows the capitals terminator in the last paragraph following the closing punctuation even though the capitals passage indicator occurs after the opening quotation mark. (This placement may just be because it's a series of capitalized paragraphs so true nesting isn't possible, but the code doesn't explicitly state that). As a counter example, UEB 8.6.2 shows the capitals indicators nested within the opening and closing quotation marks in the first sample sentence.
While Duxbury's treatment is technically correct, my preference would be to close the capitals before the closing question mark as follows:
Please let me know if you have any additional questions!