Do any of the following:
If you opened the file recently: In Keynote, choose File > Open Recent (from the File menu at the top of your screen), then choose the presentation. Keynote shows the last ten presentations you opened.
If you know the presentation title: In Keynote, choose File > Open, then enter all or part of the title in the search field. To narrow the search, click the pop-up menu at the top of the Open dialog and choose where you want to search, or click your home folder or presentation folder in the sidebar on the left. When you locate the presentation, double-click the presentation to open it.
Tip: To see where the file is saved on your Mac, select the presentation in the search results; the file path to its location is displayed at the bottom of the search results.
If you don’t know the title, or you want to search email attachments and presentation content: Click the Spotlight icon in the menu bar in the top-right corner of your screen (it looks like a magnifying glass), then enter one or more words from the title or from the presentation content. In the search results, click the presentation to see a preview of it. To open the presentation, double-click it. To see where the presentation is located on your computer, hold down the Command key and double-click the presentation.