"All over the place" can be a literal expression, meaning "everywhere" or "all over the world." However, you are talking about its figurative use, about a mental state, or a pattern of chaotic activity. It can be applied to individuals. However, you would not usually describe yourself that way. Be aware that this is an idiom, and it is informal. It is a negative judgement. It is a criticism. It means that something is inconsistent, disorganized, careless, or hasty. The speaker usually means that something is a problem that can and should be corrected. "[Politician X] has been all over the place on [issue Y], which is what happens when you take a serious subject, and treat it with farcical superficiality..." Politician X needs to set a consistent and intelligent policy. "A new rumor about a test screening of a movie describes the film as 'all over the place' and 'confusing.'" The movie needs to be fixed. "Muni-bond ratings are all over the place. Bond-ratings firms are struggling to judge the creditworthiness of cities with deep financial problems. There have been widely disparate ratings and errors in analysis..." The same bonds are being given good ratings by some firms and bad by others. The ratings agencies are not doing their job properly. The idiom is also phrased as "all over the map." Other ways to describe the same thing are "vacillating," "wishy-washy," "chaotic." Complete changes in opinion one extreme to the other are "flip-flops." When describing yourself, you want to use a kind expression that suggests that it's forgivable, and not your fault. If you are having trouble making a decision, "I'm on the fence," "I can't make up my mind." Recently, a phrase has become popular, and I like it: "I'm suffering from analysis paralysis." In your example, "How do you feel about your parent's decision to separate," some answers could include "I feel conflicted" or "I feel torn."

The phrase "all over the place" operates under the understanding that an individual is feeling a lack of control or rather doesn't know what they are feeling. At the very least, by American speakers of English, you would be understood universally. The second example would convey that you don't know exactly what you are feeling in regards to your parents divorce, as the first would communicate that you don't have your skills for the test accurately studied, or at least studied conclusively.

The first can be used: I’m all over the place preparing/studying for my test. The second one cannot be used in this context because “over the place” describes a state not a feeling