I've never heard Japanese knives referred to in this way...
I did a Google search on "J Knives" and the first page did get some hits for Japanese knife sites and discussions, but after that it kind of went off topic.
When I saw JKnives, the first thing I thought of was a jackknife. I'm just not sure this term is intuitive enough, or widely used enough, to be a popular choice for someone who wants to start a website that sells Japanese knives. And how many people are starting sites like that?
Something else to consider... Names ending in "knives" don't seem to be big sellers. NameBio shows less than 20 sales in the last 10 years, and terms like BestKnives and SwissArmyKnives were only going in the low to mid $XXX range.
So we've got a highly targeted, somewhat unpopular niche... and a name that would be confusing or misleading. It's not a winning combination.
Reg fee for me, but maybe you'd get some takers in the $XX to low $XXX range.
Perhaps you could even try some outbound marketing to existing Japanese knife sites (if indeed the term is used in the industry). Just keep the price reasonable.