Answer: The syllable that should be accented in the word "achievement" is "chieve".
Explanation: The word "achievement" has three syllables: "a", "chieve" and "ment". However, the syllable that should be accented is the second one, that is to say "chieve". Therefore, "chieve" should be pronounced longer, louder and at a higher pitch than the other two syllables. In other words, "chieve" should be emphasized, while "a" and "ment" have to be pronounced softer.