A mesh has a geometry and a topology.
The topology is the connectivity of vertices, into edges, facets, cells.
The geometry are all the nodes in the mesh (for linear meshes, this corresponds to the vertices).
To map a cell into the geometry, you can use dolfinx.mesh.entities_to_geometry, see for instance: Getting coordinates of facets in dolfinx - #2 by dokken
Note that DOLFINx has convenience functions such as: XDMFFile.read_topology_data and XDMFFile.read_geometry_data which reads data from xdmf in parallel, and is used for mesh creation: dolfinx/utils.py at baf4b6a6c0cdbc9349c9ab93263b1b66be6669e0 · FEniCS/dolfinx · GitHub