The pronunciation of Géminard is regular, i.e. the way it is written creates no uncertainty for a native speaker.
The most common one in France would be /ʒeminaʁ/, something like “zhaymeenahr”.
There are however a lot of possible variations depending on the speaker but they shouldn’t not prevent cross-comprehension. For example é might be open /ɛ/ and even perhaps a diphthong, a might be an /ɑ/ and there are possible variants for r like /R/ or /χ/ or even not pronounced at all. The stable parts are min and the fact the ending d is never pronounced.
Géminard etymology is possibly from the Latin gemini (twin) which gave both jumeau and gémeau in French.