The Open PHACTS KNIME nodes are available from GitHub
For PC users: the full repository can be downloaded via the "Download ZIP" button on the right hand side. Unzip the downloaded file.
NB: the screen shots below were made on Ubuntu but Windows machines behave similarly.
Then unzip the "org.openphacts.utils.json_1.1.0.zip" file to a folder of the same name.
Place the newly created org.openphacts.utils.json_1.1.0 folder and its files in the Plugins folder of KNIME application
Alternatively, clicking on the "org.openphacts.utils.json_1.1.0.zip" file from the GitHub page, should take you to this page: https://github.com/openphacts/OPS-Knime/blob/master/org.openphacts.utils.json_1.1.0.zip
On this page, by clicking on the "Raw" button (next to the "History" button), you can download just the org.openphacts.utils.json_1.1.0.zip which should be extracted into the KNIME plugin folder.