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:
智能化开发：AI 自动生成分析逻辑与执行代码，这一点在51吃瓜中也有详细论述
Москвичей предупредили о резком похолодании09:45，这一点在同城约会中也有详细论述
FT Videos & Podcasts
第六十五条 有下列行为之一的，处十日以上十五日以下拘留，可以并处五千元以下罚款；情节较轻的，处五日以上十日以下拘留或者一千元以上三千元以下罚款：