This is pretty weird.
I did print an assignment on a friend's computer running some weird Chinese PDF reader, the result was all kinds of weirdness. All my inserted formula for example turned into series of gibberish that can't be comprehended at all. Whack Chinese characters that I don't recognise and doesn't even exist in typical dictionaries will show up too (must use online ones that include very obscure characters).
Luckily I found out before handing it in, saved a heart attack. I used adobe's PDF reader and the print was absolutely fine.
So I think this is some kind of bug/corruption, and it happened when the book was being printed. However, why did it only affect one chapter? Maybe they had different printers printing different chapters, then it's all bound into a book? I don't know the process of printing books.
From Wikipedia:
Ê is the 9th letter of the Vietnamese alphabet and represents /e/. In Vietnamese phonology, diacritics can be added to form five forms to represent five tones of ê:
Here's how it can be typed, might help?
https://fontmeme.com/alt-codes-shortcut ... haracters/
Maybe it's a typo? I think details of the book, such as the date it was written and/or printed will help as well.
Here's Times New Roman VS Calibri. The hook is placed differently.

