The short answer is that you cannot copy a column from one type (project, task, issue, etc.) of report to another. But there are ways to get the same information that was in the second report into the first. It depends on the report type and the information desired.
A task report can have specific information about a list of tasks on individual rows. But a project report will list all tasks as a collection in one field. if you want info about specific tasks, you have to name them specifically.
Can you give an example?