The answer is #"not very"#. And does benzene contain functional groups that would confer some degree of aqueous solubility? The answer is NO....
Benzene is a carbocyclic ring consisting of non-polar #C-C# and #C-H# bonds. Aqueous solubility is unexpected. It is SLIGHTLY less dense than water, so it would sit atop an aqueous solvent in a phase extraction.
On the other hand, phenol, #C_6H_5OH#, i.e. benzene with a pendant hydroxyl group has some solubility in aqueous solution, and also elevated melting/boiling points compared to the parent benzene molecule. How would you rationalize these properties?