Save the scene as a DSON User File (*.duf), which is DAZ Studio's internal format.
We will call her Maria, so we choose the file name maria.duf. Also rename the character in DAZ Studio. This is important because this name will appear in Blender, and we don't want all our characters to be called Genesis 8 Female.
The .duf file contains information about the character shape in the form of morphs, but I have not fully understood how this is implemented, and in particular not how clothes are fitted to morphed characters. Instead of trying to reproduce the final vertex and bone locations inside Blender, these basic data are exported by a custom script to a .json file, which is then used in Blender to recreate the final meshes.
Important: To make meshes look the same in Blender and Daz Studio, save the scene at high resolution but export the json file at base resolution.
The reason is that final vertex coordinates depend both on the applied morphs and on mesh smoothing, as explained in https://diffeomorphic.blogspot.com/2020/03/mesh-fitting-without-spurious-smoothing.html. By switching to base resolution the unwanted smoothing effects are eliminated.
First make sure that the DAZ Studio plug-in is installed, following the instructions here. From the File menu, select Export Basic Data.
Export a .json file with the same name as the .duf file, and located in the same directory. Since Maria lives in the file maria.duf, the file name becomes maria.json.
After a little while we receive a message that the file has been saved. This concludes what we must do on the DAZ Studio side.
In earlier versions the information was transferred using Wavefront (.obj) or Collada (.dae) files instead. However, these standard formats have some problems, and it is no long possible to use these pipelines in version 1.3.