For example i want to convert the following shape :
to a group of paths so i get path points in all edges.
Extensions → modify path → convert to dashes does exactly what you want.
You could always use Path -> Stroke to Path and although that would convert the shape into a single path it does give you nodes on all edges like you asked for.
Finally i got the answer it was very simple, sitting there in front of me, but for some reason i didn't catch it!, anyway here is the solution :
1) draw a circle for example.
2) Remove fill color.
3) Set stroke color.
4) Choose dashes type from stroke style with the appropriate width
5) From the main menu click on Path > Stroke to Path
6) That's it.