Settings > Notifications > "In Notification Center" > Messages > Then "On/Off", Alert style, etc.
Having said that the default is on and it should display on your home screen (not your lock screen unless you've turned that feature on) when you swipe from the top. If everything looks okay you might want to try resetting your iPad:
Reset the iPad: You can do this by pressing the Home button and the Sleep/wake switch on the top the iPad's case and holding them down together for at least 10 seconds, until you see the Apple logo. The iPad should then reset itself. The boot up process takes a few minutes and then the iPad should be responsive again. More here:
iPhone, iPad, iPod touch: Turning off and on (restarting) and resetting
Hope that helps!
Your question deserves it's own thread so we'll move it to the iPF Help area for a better response.