How to ask what personality traits do you like in Mandarin
I've seen it translated as: 你喜欢什么个性特征 but isn't 性特征 sexual characteristics?

Here 个性 as personality, 特征 as traits
There is actually a difference

你喜欢什么东西? - Which thing do you like.
你喜欢什么个东西? - Why do you like it.
你喜欢个什么东西? - Same as 1.

In 0, you don't know what they like and you want to know.
However, in 1. or 2. you know what they like but don't understand why, and likely  because you don't like it. But sometime 1,2 means the same as 0, it still depends on the context.

So I wasn't sure if it would be better to use 人格特质 in place of 性特征?

It really read as 什么(个性)(特征), not 什么个(性特征), so we can change 个性特征 to
人格特质 or just 个性 in short to avoid the confusion.

How to ask what personality traits do you like in Mandarin

你喜欢什么性格