I'm telling you, SOMETHING did happen at school today, even if your child won't tell you about it. There are tricks to getting a different response.
These links both offer ideas, and I promise you won't feel cheesy or forced with these questions. The best part about this is also once you do this regularly for a couple weeks, this will just happen spontaneously. I promise you too will get more than a grunt and a shrug in response to you "How was your day?"
Another link for you: This is a previous post of mine, sharing thoughts about connecting with your kids, maybe some steps to take, or processes to adopt, and things to focus on to make your interactions that much more positive and fulfilling.