What size spanner/socket do i need to get the sump plug out of my 2.6 litre 1993 magna wagon?

for a TJ magna its 24mm

its probably the same....

You also need to make sure you use a hex socket (six sided) not an ordinary 12 sided socket. Magna sump plugs tend to get real tight with age (or some ham fisted grease monkey over torques it) and you can easily round the bolt head with a 12 sided socket. Been there done that!

confirm 24mm in size, never had one i couldnt undo with a spray of RP7 and some effort. just dont use a super nasty spanner on it if it's real tight or you might snap the head off causing many swear words ( i love it i have understanding neibours :D)