How to say "dull the knife"? I want to translate "Using the knife on these types of surfaces will dull the knife." This I find to be difficult grammatically as well. However, I'm not sure how to say "dull" in Mandarin, and google doesn't provide much help.
Dull (adjective) as in 'a dull knife' is 钝 in Mandarin. There is not a two-character version for it.
Dull (vt.) as in 'dull the knife' is 使..变钝, literally 'make .. become dull'.
Example of 钝 (adjective):

It's impossible to cut a pineapple with such a dull knife.
用一把这么钝的刀子切菠萝是不可能的。

To translate your sentence, which is also an example of 使..变钝:

Using the knife on these types of surfaces will dull the knife.
在这些类型的表面上用刀会使刀变钝。

Related words:

(Knife or blade) sharp (adjective): 快 or 锋利.

快 must be used in the same sentence as the noun (刀), otherwise it doesn't mean 'sharp'. 锋利 can be used standalone.

Sharpen the knife (V+O): 磨刀.

An example using all these words:

刀子用多了会变钝，磨一磨就又变快了。
Knife becomes dull after some use. Burnish it and it will be sharp again.