UPD. Нет, пардон. JSON валидный на первом уровне:
{'text': 'нажми на это сообщение',
'bold': True,
'color': 'dark_red',
'clickEvent': {'action': 'run_command',
'value': '/give @p written_book{pages:["{\\"text\\":\\"нажми на это сообщение\\",\\"bold\\":true,\\"color\\":\\"dark_red\\",\\"clickEvent\\":{\\"action\\":\\"run_command\\",\\"value\\":\\"/give @p oak_sign{BlockEntityTag:{Text1:\\\\\\"{\\\\\\\\\\\\\\"text\\\\\\\\\\\\\\":\\\\\\\\\\\\\\"нажми на это сообщение\\\\\\\\\\\\\\",\\\\\\\\\\\\\\"bold\\\\\\\\\\\\\\":true,\\\\\\\\\\\\\\"color\\\\\\\\\\\\\\":\\\\\\\\\\\\\\"dark_red\\\\\\\\\\\\\\",\\\\\\\\\\\\\\"clickEvent\\\\\\\\\\\\\\":{\\\\\\\\\\\\\\"action\\\\\\\\\\\\\\":\\\\\\\\\\\\\\"run_command\\\\\\\\\\\\\\",\\\\\\\\\\\\\\"value\\\\\\\\\\\\\\":\\\\\\\\\\\\\\"/title @a title {\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"text\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\":\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"ТЫ ПРИЁМНЫЙ\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\",\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"bold\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\":true,\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"color\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\":\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"gold\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\"}\\\\\\\\\\\\\\"}}\\\\\\",id:\\\\\\"Sign\\\\\\"}}\\"}}"],title:"Custom Book",author:Player}'}}
А дальше разворачивайте сами=)