The specific fallacy in this question is known as Complex Question (sometimes referred to as a loaded question). A complex question is one that contains a presupposition that may not be true, which forces the respondent into a position where they cannot answer without conceding something problematic.
In this scenario, the lawyer's question assumes that the witness had a plan to defraud the company, which is an assumption that may not be true. The question implies guilt by presupposing the existence of a fraudulent plan without any evidence to support that claim.
Regardless of how the witness answers, the question puts them in a difficult position. If the witness responds affirmatively ("Yes"), it can be interpreted as an admission of guilt, suggesting that they did, in fact, have a well-thought-out plan to defraud the company. If they respond negatively ("No"), they may unwittingly imply that there were some aspects of the plan that were indeed well-thought-out, but they are just claiming they did not have a plan.
Overall, the complexity and loaded nature of the question means that it unfairly manipulates the witness's response and biases the situation against them, regardless of their answer. This is why the question is deemed problematic and unfair.