What does 膝盖 mean in this context?
It comes from a net slang &quot;给你跪下了&quot;(I'm kneeling down to you) or &quot;给跪&quot; for short, to show one's admiration when something is far beyond his ability.

你能吃六碗饭？我给你跪下了！
你微积分考试得了满分？给跪了。

And this has variants like &quot;献上我的膝盖&quot;, &quot;给你我的膝盖&quot; or &quot;膝盖给你&quot;, where &quot;give you my knees&quot; just means &quot;kneel to you&quot;. So basically you can take 膝盖 as a metaphor for admiration, e.g.请收下我的膝盖