The best opening line when breaking the ice is to find something in common with that stranger at the event.
Start with ‘Please may I join you?’ or ‘Please may I introduce myself?’
Exchange names then ask one of these:
“Where have you travelled from?”
“How was your journey here?”
“What are you hoping to gain from this event?”
“Who is your host for this event?”
“Have you been to this venue before?”
“What made you decide to come tonight?”
Try to avoid at the start ‘What do you do?’ as I believe starting small talk is a great way to kick start a business relationship but from a common perspective.
The “work” can come later…