Using XMLStarlet to get the `value` of the `prop` with `name` "`one thing`":
$ xmlstarlet sel -t -v '//prop[name = "one thing"]/value' -nl file.xml
2
This applies an XPATH query to the XML which selects the `value` node(s) beneath the `prop` node(s) that has a `name` node with value `one thing`, and then extracts those nodes' value.
I used `//prop` for brevity, which would find `prop` nodes anywhere in the document. You could change this to `/conf/prop` if you know that the `prop` nodes that you are interested in are always to be found under the root `conf` node.
The same thing with `xmllint`:
$ xmllint --xpath '//prop[name = "one thing"]/value/text()' file.xml
2