To vote for the hubnugget nominations, you can go to The Hubbers Hangout in the Forums. There also is usually a link at the top of the forums page each week that is highlighted in blue along with the weekly topic inspiration and any other contests posted by Hubpages.
The hub of the day is not a voting hub. The hub of the day is selected by an HP employee. To read it you can simply click on the hub and then leave a comment if you wish. Hope this helps!