What I found is that written evidence for knocking on wood (and for the history of gesture as a whole) is remarkably sparse. In the Penguin Guide to Superstitions, folklorist Steve Roud offers a skeptical take on the provenance of knocking on wood due to the near total absence of written records about it:
Цены на нефть взлетели до максимума за полгода17:55。关于这个话题，heLLoword翻译官方下载提供了深入分析
Жители Санкт-Петербурга устроили «крысогон»17:52。关于这个话题，旺商聊官方下载提供了深入分析
车企密集从华为系抢人，目标非常明确：引入华为IPD、IPMS流程，大刀阔斧改革传统的产品研发以及销售体系。。关于这个话题，雷电模拟器官方版本下载提供了深入分析