Nuclear gyromagnetic ratio is a constant. I'm not sure if it shows up in Gaussian logfiles, but you can i.e. find it here: http://kodu.ut.ee/~laurit/AK2/NMR_tables_Bruker2012.pdf (Tables 8-13)

Dear Adam, thank you so much for your help. The whole problem is shown in the following picture. I want to get Hyperfine Coupling Constants. Thereinto there are two parameters, Fermi contact analysis(Bf) and the nuclear gyromagnetic ratio(gl) to be solved by Gaussian. but I don't know where is the data about the nuclear gyromagnetic ratio(gl) in the output file.

Dear Adam, thank you so much for your help. The whole problem is shown in the following picture. I want to get Hyperfine Coupling Constants. Thereinto there are two parameters, Fermi contact analysis(Bf) and the nuclear gyromagnetic ratio(gl) to be solved by Gaussian. but I don't know where is the data about the nuclear gyromagnetic ratio(gl) in the output file.

Hi there. g_J can be calculated, but still, this corresponds to the tabulated gyromagnetic ratios. I think that probably after the last sentence in your piture a kind of table for the gyromagnetic ratios is included in the script? in principle it would be possible to calculate the values in the way described, yet the nuclear spin as well as the magnetic moments are constants for a given nucleus or ion, thus even Gaussian will use the tabulated values. The Fermi Contact Part B_F is computed by Gaussian and is the actually interesting values here.