"Juice of one lemon" just means "lemon juice to taste." If the recipe required precision, it would be written more precisely.

Obviously that depends on the size of the lemon. You can probably fit about 376 of the small ones in your bottle, and four of the big ones

as someone who has juiced a lot of lemons one standard lemon is usually around 50-60ml, limes are usually 30ml

If it's the same lemon-shaped bottle of lemon juice I'm thinking of, it should say how many tablespoons of juice equals a medium lemon (Something like 3TBS maybe? Too lazy to look in my fridge right now)

Agreed. But this is where (and I'm gonna get shit on for suggesting it) Google's AI answers are super handy. "Average lemon juice yield" and you'll have a reasonable answer.