The ear is analog. So there's no defined sampling rate (a digital restriction) that would match best with what humans hear. The typical approach here is empirical testing. Luckily, most of that work has been done already, and you can just pick one of the higher standard sampling rates. (It's best to pick one of the standard rates, since most hardware is configured for those rates).
Wikipedia lists some of those standards:
Sampling rate used by some professional recording equipment when the
destination is CD (multiples of 44,100 Hz). Some pro audio gear uses
(or is able to select) 88.2 kHz sampling, including mixers, EQs,
compressors, reverb, crossovers and recording devices.
DVD-Audio, some LPCM DVD tracks, BD-ROM (Blu-ray Disc) audio
tracks, HD DVD (High-Definition DVD) audio tracks. Some professional
recording and production gear is able to select 96 kHz sampling. This
sampling frequency is twice the 48 kHz standard commonly used with
audio on professional equipment.
Sampling rate used by HDCD recorders and other professional
applications for CD production.
DVD-Audio, some LPCM DVD tracks, BD-ROM (Blu-ray Disc) audio tracks,
and HD DVD (High-Definition DVD) audio tracks, High-Definition audio
recording devices and audio editing software. This sampling frequency
is four times the 48 kHz standard commonly used with audio on
professional video equipment.
Clearly you could just pick the highest frequency you can get. But there are other considerations. Primarily, the hardware being used to playback the audio. Typical configurations for PCs are usually around 96 kHz. The most common sound card out there is the Realtek HD Audio and its manual lists its typical rates:
44.1KHz: This is recommend while playing CD
48KHz: This is recommended while playing DVD or Dolby.
96KHz: This is recommended while playing DVD-Audio.
As with many things in software (and "IRL"), it's a balancing act. If your game has audio as a primary features, you'll want to include high quality sound but you may want to keep the storage requirements low too. The production of higher quality sound is also typically more expensive, with higher equipment cost and more processing times.
In my opinion, 96,000 Hz is enough.