IMDb has set up a page for the event here. You can go there and use their twitter link to ensure that your question gets to the correct hash tag. It is not clear if they will also run the event from this page. Right now they are flashing some of the question-tweets that folks are submitting.
Update: You can o to the link above and you will see the question asked with Keanu’s answer next to it.
You can also follow the live feed on twitter here.