Hehe, the point is the "g" or "k" should not be silent if you actually want to pronounce "GNU" or "knee".. but in English they generally are. In other languages the sound produced is a more guttural but fully enunciated word (if I knew more linguistics I'd find the international phonetics for it).

The <k> in “knee” is silent; it is pronounced /n i/, not /k n i/.

The reason this cluster is so difficult for Anglo-Saxon is exactly because English lacks it; it historically had it, which explains the many words that are written as such, for etymological reasons.

Even the actual word “gnu" is pronounced /n u/, not /g n u/, but the “GNU operating system” is typically pronounced /g @ 'n u/, in two syllables, with stress on the second.