CDK3 1 simple coding mutation/missense mutations (S106N) glioma
Good question, if you check COSMIC and search for S106N, you'll find no hit with CDK3. So it isn't there (anymore?). One possibility is that it was present in 2014, when the paper was written, and the mutation is removed in the mean time by curation.

However, if you look at genecards and look for the variants, on top of the table you'll find a link to expasy. here they cite to a paper in Nature, and in the supplementary data of this paper you'll find your CDK3 S106N mutation.