Is there a list of diacritic signs in Hindi? When you want to type a diacritic sign - is it typed before or after the letter it has to influence?
I'm asking because I'm developing a touch typing tutor and I want to develop it in Hindi. Thus, I need some help in understanding, how the typing in hindi works.

LEXILOGOS Online dictionaries - Languages & Countries Looks like they are above, under and after.

In abugida scripts, like those used to write Hindi and Thai, diacritics indicate vowels, and may occur above, below, before, after, or around the consonant letter they modify.

Source- wiki

As you asked, Usually while writing the Hindi letter, diacritics are added to them or written after writing the letter it is going to influence.

What is your OS, and what keyboard are you using?

How to Type Accents and Diacritical Marks on Your Computer Keyboard