The one that I know better than anyone else is China, or more specifically, Asia. China owns US debt to keep the dollar strong. Neoliberals love this because it depresses wages in America. There is little chance that China is ever going to sell their dollars - that would torpedo their trade surplus. They might make some change with the petro-yuan, but they've tried something like this before without much success.

It's also important to remember that the national debt is a product of public policy. This is a bi-partisan policy made by the top 1%. If the top 1% didn't want it, the debt would be wiped out by changing the rules, something that they have the power to do.

Here's a study that can help you to see just how much power the top 1% have:

Testing Theories of American Politics: Elites, Interest Groups, and Average Citizens

Here is the summary:

Each of four theoretical traditions in the study of American politics—which can be characterized as theories of Majoritarian Electoral Democracy, Economic-Elite Domination, and two types of interest-group pluralism, Majoritarian Pluralism and Biased Pluralism—offers different predictions about which sets of actors have how much influence over public policy: average citizens; economic elites; and organized interest groups, mass-based or business-oriented.
A great deal of empirical research speaks to the policy influence of one or another set of actors, but until recently it has not been possible to test these contrasting theoretical predictions against each other within a single statistical model. We report on an effort to do so, using a unique data set that includes measures of the key variables for 1,779 policy issues. Multivariate analysis indicates that economic elites and organized groups representing business interests have substantial independent impacts on U.S. government policy, while average citizens and mass-based interest groups have little or no independent influence. The results provide substantial support for theories of Economic-Elite Domination and for theories of Biased Pluralism, but not for theories of Majoritarian Electoral Democracy or Majoritarian Pluralism. (emphasis mine)

See? "Economic Elite Domination" is well supported by the results of the study. Now the study is not that old (2014), and it stretches out over 20 years and tests against 1700 political issues in the United States. This is influence observed from across the political spectrum at the very top of the American economy.

Bottom line is this: Whether or not America "owes money to another country", or if it will "pay its debts" is not a matter of economics. It is purely a matter of public policy, and that policy is decided by the people who already have the most money in America, perhaps the world. They are untouchable in the current political climate. Until those people change their minds, they die, or blow away, this dynamic isn't likely to change for the foreseeable future.