You can set Keynote to flag spelling errors as you enter text. You can also quickly find suggested spellings of a word.
Tap 
, then tap Auto-Correction.
Turn on Check Spelling.
Misspelled words are underlined in red.
Tap a misspelled word, tap Replace, then tap the correct spelling.
If you don’t see suggested spellings, tap the right arrow, tap Replace, then tap the correct spelling.
Tap , then tap Auto-Correction.
Turn off Check Spelling.
If you don’t want words to be corrected as you type, turn off autocorrect. See the task below for instructions.
When autocorrect is turned on in iOS Settings, misspelled and unknown words are automatically corrected as you type. Turning off autocorrect applies not only to Keynote, but to other applications where you type text, such as Mail.
Tap Settings on the Home screen, then tap General.
Tap Keyboard, then turn off Auto-Correction.