When you add a table, its placeholder name (Table 1, for example) is hidden by default. You can show the name and edit it. No tables in a presentation can have the same name.
Go to the Keynote app on your Mac.
Open a presentation with a table, click the table, Control-click the row number for row 1, then choose Show Table Title or Hide Table Title.
Go to the Keynote app on your Mac.
Open a presentation with a table, triple-click the name at the top of the table, then type a new name.
To enclose the table title in a border, click the table, then in the Format 
sidebar, click the Table tab. Click the Table Outline pop-up menu, choose an outline style, then select the Outline Table Title tickbox.
To add a caption or label to a table, see Add a caption or title to objects.