I am looking for a data set that I can use to learn ArcGIS knowledge. I tried to find one from ArcGIS online and could not find one that is suitable. If a data set from UK I would much appreciate.
Did you try this:
https://www.ordnancesurvey.co.uk/business-government/tools-support/open-data-support
Try searching the keywords 'open gis' in the search engine. Usually, you'll get open-sourced datasets that are downloadable.