Click the icon to show/hide the highlighted search results hit in the image of this page. if the icon is gold, keywords are highlighted in the item.
Note: There is a known issue where the Highlight Keywords feature does not work on items formatted as Newspaper if the original search was an Exact Phrase Match.
As a workaround, note the title of the item and perform a new search that is not an Exact Phrase Match.
Then use the filters and facets to narrow down the search results to the item you want (e.g. select Newspaper under the Format filter and enter the date of the issue in both the To and From fields in the Date filter).
Viewing the item using this search method should make the Highlight Keywords feature work as intended.