Hi.
Have you already looked at this example?
https://demo.zoomcharts.com/net-chart/examples/filters/highlight-path.html
Well you probably know the child and parent nodes. That part sounds correct that you should set link color to the child and parent links. But I'm not sure about the part about web service traversing through the nodelist.
Anyway, what I would probably do is following:
I know the child node ID (searched one), correct?
The node contains all it's links.
If you know the linkID, you can use this API method:
https://zoomcharts.com/developers/en/net-chart/api-reference/api.html#getLink
If you know the nodeID, you can use this API method:
https://zoomcharts.com/developers/en/net-chart/api-reference/api.html#getNode
So (looking at your diagram) if you get to a parent node (say, level 2), you need to find it's parent link and not the links that goes to other child nodes and only highlight that one.
Basically you shouldn't travers through all the nodes, but start from the child node (searched one) and move upwards using it's connected links and nodes.
If you still are unable to solve this, an example in jsFiddle or something like that would help.