Train watching between Jackson, MS and Memphis, TN - Trains Magazine
Closest thing to you with any significant volume is BNSF (ex-Frisco) going through Holly Springs. There may be some desultory action on Mississippi Central, which goes from Oxford through junction with BNSF up to Grand Junction where it interchanges with the ex-Southern.
Some interesting traffic further west from Oxford on the north-south IC main; you'd go west on 6 to 51. I would have to test out some potential spots and get GPS or route markers for you along here.
Pity there is not much action remaining in Jackson TENNESSEE which at one time had 5 railroads and some interesting through trains.
An obvious spot in Memphis is 'Channel 3 drive' just south and west of where I-55 turns to go over (and parallel to!) the Frisco and Harahan bridges. From there you can walk out on the 'Great River Crossing' and be safely just feet away from the south Harahan track...
A canonical Memphis watching spot is Kentucky St and "Broadway" which is just west of where Amtrak crosses all the bridge traffic at grade. This used to have many tracks and a 5mph restriction with stop signs (!) but has now been rationalized. For some reason there's never a train here when I go, but there is one at Channel 3 drive ... go figure!
There should be more traffic on the connection on the CN's IC freight line between Poplar viaduct (on the north) and the connection to ex-L&N CSX off Warford St at Chelsea in the south. Trains tend to lay up going north and east with their power just east of Cox St. off Central, but you have to sneak a bit on private property to get even a partial view of the power. It is a bit difficult to get near the IC tracks north of this (up to where it joins the 'riverfront' route via Central Station that Amtrak uses four times a day), but there are a couple of interesting locations. South there is access through the Riviana Foods plant (although you wouldn't guess this unless you actually started through it!) to good views for both watching and photography.
Perhaps you'll still find one of the hump engines at BNSF Tennessee Yard in faded Warbonnet colors, or 1837 near the Kellogg plant in old BN green with a white face ... how many years has THAT been?
