I've searched a lot but didn't find an answer: When editing lines with QGIS, I often need to split a linestring exactly on one of his existing internal vertices, but I can't find a way; I've tried the tool "Split Features" thinking that it could snap on vertices, but I was wrong, and I've tried several ways of selecting the vertex with no luck... any solution?
In Snapping Options (Settings menu) enable snapping (better snapping to vertex only in your case as suggested in comments) for your layer, then using Split feature tool make a left click on the one blank space on side of the line, then make left click on the vertex where the split should occur and in the end make a right click on the blank space on the other side of the line.
With edit enabled I found the best option was to select the line you want to split with the select single feature tool.
then with the split features tool from the advanced digitising tool-bar double (left) click to one side of the line and then double click (left) on the node, obviously having the snapping tool selected for the layer with a tolerance will select the node, then single right click to finish the cut you will see the selected line will stop at the node. Use the select single feature tool to check topology is correct.
You might want to check the snapping tolerances as well. If they are on zero it can seem like snapping doesn't work properly.
Thanks and hope this helps.