Chainline - it sounds like you are using a standard fix gear hub and the outer chainring of a double crankset. If all is to spec, the spider of a double chankset (ie midway between the two chainrings) should line up with the cog. Now, if this is the case, you can replace the bottom bracket spindle with a shorter one intended for fix gear/single speed use.

A mickey-mouse but solid way of improving your chainline would be to move a washer or two from the right side of the rear axle to the left side. But then you have to dish the wheel a little (tighten the right-side spokes and loosen the left side spokes)

Don't mess with the cog and lockring. If you ruin the threads, the entire wheel is now junk. (You may not fare much better.) Consider where the cog sits on the hub a given, then tweak where the chainrings sit or the hub sits. For the chainrings you have several good, solid options. A different bottom bracket spindle is one approach. Another is to move the chainring from the outer position on the spider to the inner position. You could do that and space the right bottom bracket cup out with a washer to move the chainring closer to where the middle of the spider was, if indeed I am right about this being a converted road bike with a double crankset.

Ben