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:
Source: Computational Materials Science, Volume 266
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Гангстер одним ударом расправился с туристом в Таиланде и попал на видео18:08。关于这个话题，91视频提供了深入分析
Маргарита Щигарева