Many theories and models describe the various cognitive processes individuals engage in as they solve ill-structured problems. While diverse in perspectives, these theories and models uniformly agree that essential aspects of complex problem solving include iteration and inquiry. This paper further argues that an important yet overlooked component of knowledge construction during problem-solving is the ability to ask meaningful questions. What is needed, but not adequately articulated and validated, is a theoretical taxonomy of question-asking to better understand and guide a learner's reasoning process. Based on the expert--novice literature, we proffer the following question taxonomy: shallow/simple (verification, disjunctive, concept completion), testing (example, feature specification, quantification, definition, comparison), and deep/complex questions (interpretation, causal antecedent, causal consequence, goal orientation, instrumental/procedural, enablement, expectation, and judgmental). We, therefore, build on existing theories/models of problem-solving, failure, and reflection and their implications towards a taxonomy of question-asking. Given this taxonomy, researchers and designers can better understand learners' level of understanding and problem-solving trajectories.