I can pretty much promise you won't like my answer.
Without significant training and practice, a knife is one of the worst self defense tools you could possibly have or use.
You would be better off getting a cane or hiking staff and learn stick fighting, if you cannot have a firearm for whatever reason.
For one thing, you have to get way to close (as in "with-in their reach") to your opponent to even use a knife.
Also, in most jurisdictions carrying a knife as a "weapon" is illegal. If for some reason a PD Officer asks you why you have that knife and you say "For Self Defense, Sir!" You are likely to lose your knife, and spend time in jail until your bail (if granted by the Court) is posted.
You might also want to consider that even if you "win" a knife fight, (truthfully there is no "winner" in a knife fight) and it was a legal case of self defense, (and they will do there best to make it look like you started it, and the bad guy or girl was defending him or her self from you) you still may not win the legal battles that will take place afterwards. In addition to probably standing trial in a criminal case against you*, the legal battles will also include the "person" you defended yourself against for injuries and medical bills if he or she lives, or their next of kin for "wrongful death" if he or she don't survive, or the "person" you defended against lived, but is now a vegetable, they can and will go after you for damages based on that.
Don't believe what you see in the movies, on TV, or those Cold Steel videos where they show what an effective "weapon" every blade they sell is, concerning the effectiveness of a knife for self defense.
*Depends on the attitude of the DA, and the results of the police investigation. By the way, the police investigation will include a whole bunch about you. Probably more about you and your past, than that of the "person" you were defending yourself against, and the events that took place before, during, and after the altercation, if you want to know the truth.
Trust me on that. Been there; Done that. In my case it helped some that there were witnesses who confirmed he shot first, not me. (my .45 made a lot more noise than his .380 did.) It may have also helped that he was a known gang-banger, and "had a record a mile thick". (I did not know about his gang activity and extensive record until long after the incident. Not that it would have made a difference in my response to him shooting at me, had I known.)
The DA (who was vehemently anti-gun) didn't like it, but she ruled I acted in self defense.
My advice is: Don't get any knife for self defense.
