Core training

Without knowing where you are starting, I'm just going to give a more generic advice. Train all of your core, not just your abs. Train extension/flexion and resistance to each. Train rotation and anti-rotation. planks, side planks, L-sit (and progressions) superman, hollow body (and progressions), wood chops, knee raises(done properly), levers (and all progressions)
Unilaterally weighted carries of various kinds.

A good, full-body strength training program works the core well, so that's generally what i'd recommend, as opposed to piecing together your own routine. What is your goal or reason for wanting core exercises?

I do 20 mins of abs 3-4 times a week and I definitely feel an improvement and some days I think I even see one too haha. I do 5 minutes of planks (45 seconds on, 15 off), I use a contraption at my gym that has you sit low on a seat and lift/throw a weighted ball at a target, hanging leg lifts, bicycles, reverse crunch, regular crunch and sometimes russian twists. Do a couple sets of 10-15 of each.

lorrpb wrote: »

TRX suspension trains your core with every exercise

I think a suspension trainer is a good choice for engaging the core. It's worth mentioning that TRX isn't the only option, there are plenty of other suspension trainers on the market. Woss, Jungle Gym XT and others.