Hmmm. Instead of the "ONE" knife, why not focus on the 90% knife. That one knife that you can and will carry 90% of the time as your primary EDC. Then you use the other 10% of carrying time for those special occasions, special circumstances, and just because times.
I'm guessing that most folks here pretty much carry more than one pocket knife most of the time anyway. So find that EDC combination and then figure out your primary 90% knife.
I pretty much always carry one slipjoint as a primary in one front pants pocket and a battered SAK Classic in the other. The Classic gets used for the scissors, which lost the spring and toothpick sometime ago and have not been replaced yet. It also gets detailed for opening taped packages so my other knives don't get gunked up from the tape. When working I have on my duty belt the Queen BEM folding hunter I have mentioned often, and a KABAR TDI on my off side specifically for weapon's retention/last ditch and no other purpose.
For several months now I've been carrying the same single blade jack as my primary. For that matter it has always been a staple in rotation. It is this simple Queen. Stainless blade with some grind marks still in it. The Delrin Winterbottom scales have a tiny crack on one side from the pin to the bolster. Crack and grind marks can be seen in the pic below. It has a strong spring. It walks and talks, full with half-stops in a crisp and precise manner. It also has some sentimental value. When I first got started on this forum and settled down in this sub-forum besides all the encouragement and welcome I got, one of the forum members seemed to be determined to help me get started on the road back to slippy. Charlie/Waynorth sent me some sharp things. Along with the ones I knew he was sending he always seemed to toss a few extras in each package. This little Queen was one of them as was the Precise fixed blade in the pic below. Both knives may not be the high end factory or custom pieces that get drooled over, but each is a well made, excellent cutting tool that takes a keen edge and can be brought back with little trouble. They don't last as long as D2, but they do stay sharp longer than a SAK. Enough to be quite usable. If I stropped each day I doubt I'd need to hit a stone much ever short of a major cutting run. The blade size is just big enough to cover most chores for me. The knife is trim, light, and carries beautifully in a pocket. On top of that the shape and feel of it is excellent for just handling. By handling I mean for sticking your hand in your pocket and just fondling the thing. You may just roll it a time or two in your pocket, or you may take it out and use it like a worry stone. Very comforting and a tactile pleasure just to handle. Therapeutic if you will. It doesn't look too bad either.
I was so impressed with the little gifted Queen that I actually bought another when I saw on on eBay. Nice enough knife, but it did not have the walk, talk, and crisp action of my original. I eventually traded the one I bought to a friend and kept the original.
I have nicer knives, but I love this simple, working man's knife and would feel it's loss should it ever become so.
So now I have this excellent, general purpose, cutting tool that handles most of my cutting needs, is pleasant just to handle, carries like it isn't even there until I need it, and to top it off, it reminds me of a fine and generous gentleman who gave a little extra to get a fellow started on the road back home to traditionals. Thanks, Charlie!
Oh, and here is the pic asked for in the OP.
Remembering the generosity I've experienced I've given a few knives to some coworkers that showed an interest, sometimes taking a knife out of my pocket and giving them the knife I was carrying.
I probably have two or three other knives that would fit in the carry it always category and would be just fine in the same capacity as the Queen. I also have a couple of knives that I like to carry for slightly special days. I've even been known to have one or two that I carry for dress occasions only. Come to think of it, I got the Appaloosa bone Case I slipped in my suit pocket for the company Christmas party in a trade with Charlie.
Then of course there is the all other knives I've accumulated that I'd go nuts trying to carry each. Though I have at one time or another just because. Some of those I love to look at and handle, but they just don't carry comfortably for me. Others carry fine, but still don't make that tiny list of knives that would be what I'd carry if I left the Queen jack at home. Don't get me started on fixed blades. I have several and I can't go the the woods with them because I would want to carry all of them.
Heck, even in a fixed blade the little Precise in 440 steel would serve as a 90% or better knife. Anything needing bigger, get the tomahawk or an axe. Btw, the discoloration of the blade in the pic above is from the scan and isn't on the knife.
So after all the wordiness. Don't try for THE ONE. I don't think it truly exist for anyone who hangs out here. Try for a 90% EDC and enjoy the others for their occasions or as auxiliary support when needed.
Amos