I also doubt that many consumers even know which special products or companies have received an industrial design award.  No comma. The word "which" introduces a clause that basically  functions as the direct object of the verb "know".

Their sample was limited to only Dutch manufacturers, which did not allow them to control their findings for companies all over the world. Yes, you need a comma after the word "manufacturers". The word "which" begins a non-defining/nonrestrictive relative clause.

This could lead to a better company performance, one which is significantly attributable to marketing intensity and not significantly to industrial design intensity.  I don't like this sentence very much, but I suppose a quick way to improve it would be to add a comma and the word "one".