In all the research literature that we examined, taking both ginkgo biloba and panax ginseng together did not seem to be contra-indicated in any way.
In fact, going on the basis of traditional cultures using these supplements together, a research study done in 2002 using healthy volunteers asked to perform math tasks, showed that a combination of the two seemed to produce the best results in the cognitive function of these people. You can read the highlights of the study here: https://www.ncbi.nlm.nih.gov/pubmed/12404705?dopt=Abstract
However, most of us who like to try/take supplements are taking multiple things; if there are things other than ginseng and ginkgo that you are taking, they may interact with those or with each other in the presence of the others. It would be a good idea to involve an herbalist or a naturopathic doctor in your final choices.