Stuttering

Separate with hyphens. First phoneme repeats, including capitals. Repeat vowels if necessary.

Refer to this: Answer: How do you punctuate stammering speech?

There are exceptions. But we may be able to deal with exceptions in subbing.

“Th-Thats…” (“Th” is the first phoneme, as such, it should be the one being repeated.)

“Wh-What?” (Wh being the first phoneme, it should be the one repeating.)