How to translate "I wonder..."
Translation from English to Chinese is more a matter of capturing meaning than finding word for word equivalences. In this case, I think the best way to capture "wonder" is by saying "would like to know."

Thus, "I wonder..." becomes "我想知道..."

Translating to "I don't know" (as is suggested by Question Overflow) might be appropriate in some situations. It's not what I would use for your example sentence, but the decision is admittedly subjective.

In any event, here is a collection of example sentences in English/Chinese with the word "wonder."