just saw that there is a PR regarding this issue. It should provide the functionality I am seeking.

Since it looks like the PR you mentioned is stalled due to a lack of examples/testing, you're welcome to contribute by helping out there.

It seems to be an easy task to add some tests, since the functions are relatively simple. But I have not done a PR again, is there something to read to guide how to proceed with it?

TBH, I have not done it myself this way, but I imagine you could clone the fork used for #42, push the branch in question to your own fork, and then add your tests on top of it. Just to avoid redundant work, it would be good to communicate your plans in #42 such that everyone knows you are picking up there.

I cloned your pr and had a look at the tests. Should I modify the example repo to add field data to it, or should I create an example file for each VTKData type which would include only some field data and test them instead? Some guidance would be much appreciated! its also a learning process for me.

I don't know the details of how much as required to test this properly, but assuming that field data is stored similarly for the various mesh file types, I'd say that adding a single file with field data and reading it should suffice.