Zebrawood is open pored, so in theory it needs grain filling but I'd avoid it if possible. The open pores are probably why the glue is so hard to remove, as opposed to say closed-pore maple. The glue can hide and grip to the inside of the pores, rather than just stick to the surface on closed-pore woods.

I'd try and find a clear sanding sealer or even use shellac to fill the pores. They don't look to be particularly large and I'm not sure what grain filler would do to the looks. It would need to be a fairly light brown colour to avoid spoiling the striping, though it may help fill in some of the edge areas by the binding. But you've probably sanded, scraped and scrubbed a fair bit in those glue areas, and filling and sanding back becomes quite risky in those places. You can do it, but you'd need to be very gentle especially around the edges.

You've done well to remove the glue you have done. There's not a lot left and you wouldn't notice it from a few feet away, but you know it's there, which is hard to ignore.

I'm set up for spraying, so if it were mine, I'd probably spray a very fine brown sunburst around the edge and live with the glue in the pores. I might try and colour over the larger pore marks with a suitable colour Sharpie or maybe mix up some artist's acrylic paint.

What were your plans for an overall finish? TruOil, nitro, poly, acrylic?