For the errors you've shown above, I'll make some educated guesses based on my own exports:
ACCESSOR_VECTOR3_NON_UNIT - Blender usually only writes non-normalized normal vectors when there is degenerate geometry present, meaning a proper normal can't be calculated. In Blender's "Edit Mode", go to Mesh -> Cleanup -> Degenerate Dissolve, and it might take care of this.
TEXCOORD_0 indicates that texture coordinates (in a UV map) were supplied for a material that wasn't textured. You can ignore it, or you can save some space by deleting the UVmap for any object using a material that isn't textured.
To answer your actual question, there's no guaranteed correspondence between a Blender mesh and a glTF mesh index, but there are tools to discover the relationship once the export is complete. The way I recommend is to install a text editor called VSCode which is free, open source from Microsoft. Export your model as "Separate glTF + bin + textures" and load the text-based .gltf into the editor. Install the "glTF Tools" extension that it offers you, and it will call out the exact spots in the text file where the validator finds errors. For many kinds of objects including meshes, the names shown here will directly correspond to mesh or object names in Blender.
(Disclaimer, I'm one of the developers of the glTF Tools extension for VSCode.)
Here's a screenshot of VSCode showing unused texture coordinates in a mesh called "glassDish":