Place the sound effect exactly at the moment of realization or impact. For a classic meme feel, freeze the frame on a "snapshot" of the subject's face just as the audio peaks.
Apply a "Chaos" or "Shake" filter simultaneously with the sound effect to simulate a high-energy explosion of shock. nani_anime_meme_sound_effect_for_editing
Editing a "Nani?!" moment usually involves a combination of audio and visual cues to maximize the comedic impact: Place the sound effect exactly at the moment
Use speedline overlays or comic book filters to give the frame an authentic anime feel. nani_anime_meme_sound_effect_for_editing