I believe this is the source model
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As for exact replica, how exact?
Are you looking for measurements to apply to another character, or just to better understand how this navel 'looks'
do you want to apply it to another character?
applying it to another character is possible, but tricky.
Best case senario, the base body uses a well known and freely available Genesis 8 Female (G8F) topology. Thats good because you could use blender to isolate the belly button sculpt and make a custom morph for a genesis character. The issue then is, what chaarcter do you want to apply the belly button to. if its a G8F character, thats good, but there are still some technical challenges that need to be overcome to preserve the belly button or stomach, depending on what you want to capture, and how different the target character is.
worst case senario, this is a custom character with custom topology, meaning you can't perfectly replicate the mesh. Or, alternatively, the character you want to apply the navel to is a different topology (doesn't need to be G8F). you can try to replicate the navel as close as possible by hand placing vertexes (I would recommend a tool like Blender). But if you really want it perfect, the topology may be too high quality (G8F is as high quality as you want to get and still have a video game ready mesh, so the belly button isn't super detailed, which is ok for sculpting). This is an issue because there may be small nuances you want to capture but the target geometry (G8F or what ever character) isn't detailed enough to capture the nuances. G8F does have a solution, using a height/depth map to allow for controlling its higher resolution mesh, but just making the height map is a huge hassle and a science on its own.
Depending on why you want this character's navel, if you are trying to apply it to another character, it may actually be less technically challenging to just morphed the linked character to match your target character.