Hi,
I suspect that it is integrated on the motherboard and not a separate removable module card or if not it may look like the audio board linked below for an Asus ZN2401IC.
I realize that the following are not your model but looking at the parts list for the Asus ZN2421FGK and FGT models there is no separate audio “board” listed as there was for the 2401IC.
The audio board for a ZN2401IC looks like this so if there is something like this in your model I think that it will also be difficult to find a different brand of “board” that is compatible. It looks purpose designed.
crwdns2934105:0crwdne2934105:0
crwdns2934113:0crwdne2934113:0
crwdns2915270:0crwdne2915270:0
crwdns2889612:0crwdne2889612:0
2