Amboyna burl is typically left natural (no stain / dye). If you can get it to take TruOil, then I would suggest that you do. It’s an amazing sealant for the wood and kitchen knives can use a little extra protection in that department, both for filling and sealing any voids to keep food out and also for protection against the constant moisture these knives see.
TruOil does more than seal the wood. Yes, it seals any tiny cracks between the tang and handle. These tiny gaps are where corrosion and bacteria like to hide. But it also provides a surprisingly grippy surface when wet.
If the amboyna won’t take the TruOil (you’ll know if the first coat doesn’t cure in 24 hours) then wipe the handle down with some acetone and use paste wax.