What is the significance of"...the solitary mocker...blissful unawareness of whose tree he sat in...? pg.254

The "mocker" mentioned in Chapter 28 is a mockingbird. He sits in the dreaded Radley tree making sweet music unaware of the danger it could be in. The bird can mimic sweet music of other songbirds hence "mocker". The bird in a dangerous place symbolizes the Finch kids in a dangerous place after the pageant.