Pepsi can probably afford to run Coca Cola through a mass spec to get an idea of concentrations and even get the processed coca leaf used by Coca Cola (there’s one company in the uS with a license from the DEA).
Pepsi probably already have done this and likely Coke have done the same to Pepsi. However, Pepsi did also see what happened with New Coke and likely don’t wish to repeat that footgun of changing the formula. Plus people buy Pepsi because they want Pepsi not Coca-Cola
But the difference is Pepsi would also have had dedicated laboratories and food scientists, scientifically controlled exhaustive testing and unlimited access to any ingredient they wanted. Thus one would expect Pepsi's testing to have had much finer granularity than in this YouTube video).
With millions of dollars tied up in just a few percent of sales you can bet Pepsi knows just about as much as Coke does about Coke's ingredients (and vice versa of course).
The research for both companies is more about the fine minutiae—keeping an optimal differentiation between the two products more than treading on each other's territory. Trampling over each other for market share is done through advertising, not by making their products the same.
Pepsi probably also has had access to Coke's supply chain and long ago acquired samples of various inputs before mixing, which would make analysis easier. The two companies know they're competing mostly on production management and brand image, not secret ingredients. A decade or so ago a secretary from Coke tried to sell some of the company's "secrets" to Pepsi. Instead of jumping on the opportunity to get Coke's secrets, they contacted Coke's legal department and the FBI, with the three working together to prosecute her.
