Github user mcgilman commented on the issue:
https://github.com/apache/nifi/pull/2394
The change should be pretty straight forward. Here is an example of setting
the title on the SVG elements [1]. In this example however, the tooltip is
dynamic and needs to be regularly updated. Your tooltips will be not be
changing based on the configuration so you only need to set them when those
elements are appended starting here [2].
[1]
https://github.com/apache/nifi/blob/master/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-ui/src/main/webapp/js/nf/canvas/nf-process-group.js#L1195
[2]
https://github.com/apache/nifi/blob/6153fb64655701f7bfdaadfe1ff7c8def111422c/nifi-nar-bundles/nifi-framework-bundle/nifi-framework/nifi-web/nifi-web-ui/src/main/webapp/js/nf/canvas/nf-process-group.js#L304---
