What is the pronunciation aid that determines the stress placed upon a syllable called?

Accent mark.

Explanation:

An Accent mark or Diacritical mark is a special sign used above a vowel to indicate stress in the pronunciation of the syllable it is located on. Although the English language doesn't not include such sign in its grammar rules, there are other languages like Spanish that make use of it in many of its words.

conversing outside - a.

yuiyiy

explanation:

uiyui