Choosing a topic for a research paper can be a challenging task, but among the options you've listed, the following method is particularly helpful:
Look for repeated ideas as you research your topic.
This approach allows you to identify areas of interest that are significant and widely discussed in your field, making it easier to choose a relevant and impactful topic. By recognizing what ideas or themes recur in your initial research, you can find a topic that not only interests you but also has sufficient resources and scholarly discussion available.
While the other methods (skimming and scanning, using a web diagram, and using note cards) can also be helpful in the research and organization phases, identifying repeated ideas can provide a more focused and meaningful topic from the start.