I have this cut that I haven't really touched from 4 days ago from a swiss knife. The cut wound's edges do not meet & there's a gap. What should I do?

Keep it clean. We don't know where the cut is, but at 4 days about the only advice i can give is to keep it clean: wash it 2-3 times/day with soap and water (as my mother told me, "soap and water never hurt anyone.") if there are any functional problems: loss of motion or loss of sensation, these can generally be dealt with on a non-emergent basis. If not, this will probably heal just fine.
Location? Size? I assume that the cut is on a finger? As long as the cut does not appear infected (unusual swelling, redness, tenderness), the cut is small and you have no loss of function (movement) or sensation (numbness), then you are probably okay to keep the cut clean with normal washing, apply antibiotic ointment and cover with a band-aid. Change the band-aid daily and clean with 3% peroxide if crusty.