Train schedules

Contact the railroad public relations department or befriend a railroader.

Generally, there is no schedule.  I usually look online for local railfans, ask someone who works at a convenience store next to the tracks (other than teenage girls who never seem to know anything,) or ask at the local RR office.  Sometimes I place a deer camera at a hidden spot along the tracks and leave it for a day or two, and check to see what times trains appeared.

Kent in SD

I think you may be referring to NS' Port Road line that runs down to Perryville, MD.  As Kent mentioned; there is no published schedule.  Given this is no longer a major through route; I imagine train traffic on this line is sparse and limited to perhaps a pair of manifest trains and a pair of intermodal trains operating several days each week along with occasional coal or grain unit trains.  I'm not aware of any industrial type shippers on the line so local freights are probably nonexistent.

What I would suggest is that you simply visit the spot you have selected at different times of the day and on different days of the week.  Note what kind of trains you see and the day or time you see them.  Not all of NS' numbered trains operate daily but, by observing over a period of time, you will begin to see that intermodal, manifest freight and automobile trains do tend to show up in the same general time period on the days they run.  

While coal, oil, ethanol and grain unit trains operate with numbers on NS, they are more akin to extras and can show up any time.

If you have a scanner or can borrow one; take that with you as it will allow you to locate trains either by listening to the defect detectors broadcasting or hearing the train crew "call the signal".  Either type of transmission on NS will give you the milepost and direction of travel.  I'm not sure what the road channel is on NS' Port Road but they use 160.80 on the Pittsburgh Line.

This process will take time but, if you enjoy being outdoors, you can have an enjoyable time even if train traffic is slow.  I've had great days in the woods bird hunting or fishing where I didn't shoot or catch a thing and train watching is kind of the same thing; for me at least.

Curt

Here's a simple sure-fire way. On a hot day, show up near working railroaders on the line with a couple of ice-cold six-packs of mountain dew and coca-cola. Preferably a pizza too, but the soda usually works. Have a couple of business cards handy, with your cell number. I cannot begin to tell you how much information I have gotten this way.

I wish the OP would have been a little more specific on his desired location. The NS Port Road Branch runs from Enola Yard, south along the west bank of the Susquehanna until it crosses to the east bank at Shocks Mill Bridge.
The traffic level is less once south of Columbia, but this is still NS's preferred route to both Baltimore and Delaware.
Since much of the traffic is scheduled for night, due to having to access the NEC at Perryville, I would get out lineside  early a.m. or late p.m.

A portable scanner is your best friend, and here are some appropriate frequencies:
160.980 - Harrisburg Terminal Dispatcher
161.070 - Port Road Dispatcher/ Road channel; this is the channel that train crews will call out lineside signals as they approach.
161.445 - Enola yard

160.920- Amtrak CTEC3 Dispatcher, heard in Perryville,MD. area to allow NS to move on/off Amtrak NEC line.
Go to parailfan.com and download a HTML document of a Port Road timetable. This can be used to match locations/mileposts that you hear mentioned on the scanner, so that you gain an understanding of when train traffic is nearby.
June 2017 Railpace magazine had a good article on a new 8-mile bike trail that runs along the Port Road from Columbia north to Shock's Mill bridge.

While you're waiting by the banks of the Susquehanna, remember that railfan photography is like fishing, you might get skunked sometimes, but a little planning will help you find the "honey hole".

Great response, guys.  There is a lot of information in this thread.  Thanks to all.  I always had an interest in the Columbia & Port Deposit, where GG1's on freight were once standard.

Lionel Grandpa:

Google "NS train symbols" and you will be taken to a rail fan website that lists all current NS train symbols; the type of train; origin/destination pairing and frequency of operation.  

I just looked at it and found one manifest and one intermodal train that operate daily to Bayview Yard in Baltimore. Additionally; there are a number of coal loads/coal empties symbols that look like they would run over the Port Road.  Basically you are looking for anything destined to Bayview Yard, Baltimore, Sparrows Point, Chase and Edgewood, MD.  I'm not sure but, I would guess trains destined to Wilmington, DE may also take this line.

Now the bad news; since these trains must run over Amtrak's Northeast Corridor from Perryville, MD to reach their destinations, it is likely the eastbound trains are running over the Port Road after dark.  Amtrak gives NS a window in which to operate and it normally would be during the wee hours of the night.  Coal empties and westbound manifest and intermodal may run the Port Road after daylight given the times they would have to traverse  Amtrak's line.  This is pure conjecture but; I believe your best bet to catch a train on the Port Road would be during the morning hours.

Good luck!

Curt

Thank you everyone for the very helpful information. The spot in question is at Marietta PA just north of a Columbia. It's not in my normal travel area so I will have to stake it out and hope for the best.