WITH his marathon performance on Broadway and fathering another child, it’s a wonder Jude Law has any strength left. But the star was making out with a hot blonde at The Box on Saturday night. A spy reports, “Other guests were trying to talk to Jude, so he got a member of the staff to keep them away while he flirted with and kissed a very pretty blonde.” He has yet to meet his daughter, Sophia, who was born last month following his brief affair with model Samantha Burke. Law’s rep didn’t return an e-mail.