(Psychological / emotional perspective)
To be dreaming of a knob such as a doorknob can indicate some kind of turning point in our life.
A noticeable contrast between the door and the knob can present the dreamer with certain insights.
For instance, a very plain knob on an ornate door may indicate that the process of moving forward from a situation is very easy.
The knob coming off in our hands suggests a missed opportunity. We may need to turn or change issues or conditions.