From SOFAWiki

How to display the vertex indices using MechanicalObject

It can be handy to have a visual clue about the indices of a particular set of dof. This can be achieved by toggling the Debug : view indices check box in the mechanical object edition dialog box. To raise that dialog simply double click on the mechanical object component in the Graph tab you are interested in.

How to display topological elements using dynamic topologies

In every GeometryAlgorithms classes (PointSetGeometryAlgorithms, EdgeSetGeo..), the GUI panel allows to draw its topological elements or/and their indexes. To raise that dialog simply double click on XXSetGeometryAlgorithms component in the Graph tab you are interested in and select wanted option.

Moreover, it can be useful when topological mapping are involved in the scene. Indeed it allows to display easily either the upper or the bottom topology.

For example, in the following screenshots, fisrt image display the edges in a tetrahedron topology, whereas the second image shows the edges only from the mapped triangular topology (border of the tetrahedron topology). Finally last image shows the possibility to display edges on a triangular topology while performing incisions.