1
When did the accident occur?
To sign this, start with 'WHEN', then sign 'ACCIDENT', and finish with 'OCCUR'. Since this is a 'wh-' question, remember to keep your eyebrows furrowed and tilt your head slightly forward throughout the sentence to show you are asking for information.
2
The meeting will occur tomorrow.
In ASL, time concepts usually come first. Sign 'TOMORROW' to establish when the event is happening, followed by 'MEETING', and then 'OCCUR'. You don't need a separate sign for 'will', as 'TOMORROW' already sets the sentence in the future tense.
3
Did that really occur?
Sign 'THAT', then 'REALLY', and finally 'OCCUR'. Because this is a yes/no question, you must raise your eyebrows and lean in slightly while signing. The crisp flipping motion of 'OCCUR' emphasizes the reality of the event.