There is no such things as "the" U value for any element. You adjust the U values to change the band gap of certain materials, typically by fitting to experimental values. In general it helps people answering your questions if you provide a bit more information, such as "I need this because I'm trying to get a more correct band gap of material X, and I'm getting a too low value with LDA compared to papers I've read, e.g. PRB 123, 222xx (1995)".
Now, you don't strictly need the material to have d-orbitals to use a Hubbard model, but the theoretical background kind of assumes that the band gap changes due to an improved description of the localization of d-electrons.
