At the stern, where it would also be deployed from if ever needed -- which again is unlikely...
In theory it could also sit on top of the potter's cabin at the bows, but then you'd have to get there in a hurry and deploy it from the small bow deck -- much safer to do it from the stern. Bear in mind this isn't an ocean-going vessel which needs to anchor regularly, if something ever goes wrong on a river (e.g. loss of power) then you could be going upstream or downstream so the odds of the anchor being at the "right" (upstream) end are 50:50, and if you deploy from the "wrong" end the boat will swing round.
You could say this is not ideal, my response would be that very few boaters on narrowboats ever have to deploy an anchor in an emergency over their entire boating career, and it's more important to have one that's suitable for the boat (probably a Fortress) and be able to deploy it safely -- in my case, from the stern -- than worry too much about which end of the boat it's at.
No doubt Alan or someone else with a lot of maritime experience will come along to tell me this is all wrong, but then I'm not going to be regularly mooring a yacht off a rocky lee shore in a gale... 😉