What kind of reaction is represented by #H_2O + ZnO -> Zn(OH)_2#?
This is a synthesis reaction, also called a combination reaction.
A synthesis reaction occurs when two or more reactants produce a single product. The general equation is A+B
In your question, the reactants (A and B) are water and zinc oxide, and the product (C) is zinc hydroxide.
Note: I don't believe that the reaction in your question actually occurs, but the equation in your question is set up as a synthesis reaction.
To denote a reaction that does not occur, you would write A+B