128 million Americans saw it in theatres when it came out apparently (that's just Americans! And just the initial theatre release). But it's been shown on TV, streaming services, etc (and you could pirate it of course) and is accessible in pretty much every country today. There's been surveys with results like "26% of brits haven't seen Titanic", etc, but no real hard data unfortunately. But I'd wager the percentage has to be double digits. Not super high double digits, but definitely double digits.