Review any journals or diaries you have written. If you justify your actions in terms of logic and evidence (i.e. language like "I think" or "it is reasonable to believe") then you are likely to be a critical thinker. If you justify your actions based on how you feel about them, or if your prime criteria for a decision is other people's emotions, then you are more likely an emotional decision maker.
Read a list of logical fallacies. Use a website that has such a list (see resource 2). A logical fallacy is a reasoning error. If you don't immediately understand why the reasoning patterns described are erroneous, you may be more emotional than logical.
Take a logic test. Many such tests are available online. If you score well, you may be a critical thinker. If you score poorly, you may still be a critical thinker, but it is somewhat less likely.
Ask people in your life to evaluate your style of interaction. Ask whether you are more casual in social situations or whether you are more businesslike. Ask at least 10 people, and record their answers. If more people said "businesslike" than "casual," you are likely to be a critical thinker. Thinkers tend to be businesslike and formal in social situations, whereas feelers tend to be casual.
Look into your educational past. If you went to college, look at the courses you chose for electives. If you took courses in analytical writing, science or social science, you are likely a critical thinker. If you did not go to college, look to your bookshelf or Internet search history. Make a list of the most common subjects of books and websites you read. If you read a lot of technical or "big idea" material, you are probably a critical thinker. Critical thinkers tend to have many interests and to be interested in the big picture and technical subjects.