Final answer:
The observation method is useful for determining how many times a learner says, "Oh no!"
Step-by-step explanation:
The data collection method that might be useful for determining how many times a learner says, "Oh no!" is observation. By directly observing the learner in a controlled setting, a researcher can keep track of the number of times the learner says the phrase during a specific period of time or in response to certain stimuli. This method allows for real-time data collection and provides accurate information about the frequency of the learner's utterance.