remove it, and measure voltage to see what margin you'll need. but as 12V is the max voltage on motherboard, you can always put 16/25V anywhere on the mothertboard and be totally safe.
you can replace it with regular aluminium capacitor, or pick antoher tantalum.

for the value, it's not very critical. you can stay with 10µ like the others, or pick a higher value. not a big deal here 😀

I found some of the exact caps from an ISA riser card but it doesn't have the letter "K" on the back it's blank, does the "K" signify anything

it might just be the manufacturer "signature".
but nothing you have to worry about. just replace it with what you found, and you'll be fine. 😀

Take one with the same values like the capacitor to the left. The K means Kemet (manufacturer).

Following this ones at the photo, you should take 10uf and 16V types, tantalum. I would recommend to take 25V.
You can take any Electrolyte capacitor with 10uf and 16V (or higher) which fits the pitch.

Thanks PCE, the cap that blew was 16 volt right next to the power input would a faulty power supply be the cause for it as the motherboard was like this when I got it and wouldn't a 25 volt cap blow out after something else (add in card, motherboard components) if the power supply was faulty again I don't know components much sorry

The normal voltage range should be 12V +/-15% at most regardless of load so 16V capacitors are sufficient. They are prone to fail from old age, I had a similar capacitor fail on my 486 board (though with a lot more charring) and after replacing it the board was fine.

If you are concerned about the power supply you can test the voltages with a multimeter to verify everything is within range.