H.W.
First, you know your child best, so if there are any areas of concern, this is a good time to bring them up.
If you have no concerns about any aspects of your child's development, here are some things you might ask about:
Who does my child like to play with?
What does he/she like to do/play with other children?
Which activities does my child seem most drawn to? (I like this so I can supplement at home sometimes.)
Are there any activities during the day which pose a regular challenge for my child? (at this age, self-care and transitions can often present challenges. Teachers might suggest practicing some of those skills at home.)
Is there anything I can be doing at home to help my child have a good day at preschool? (teachers may have concrete suggestions)
How does my child play with other children? Any challenges, areas for growth? (much of the purpose of preschool is learning how to be with the other children and play in small groups, follow the group through the day)
Unless there are specific areas of concern, this is a pretty basic set of questions that can help a parent get a well-rounded sense of their child's day at school. What a great question to post.:)