Using his MTG wiki page, you can get the lore to help. https://mtg.gamepedia.com/Nicol_Bolas He's known as "second sun", which gives us krein (sun) as a possible part.

Forever Serpent (ul - eternity , vith - serpent)

the Horned One (not really helpful)

God-Pharaoh of Amonkhetor Lord Nicolas on Ixalan (rah - god, Pharaoh - drog) the Nameless after War of the Spark (no Dovahzul equivalent)

Here's the rest of the entry: ...the youngest and most powerful of the seven Elder Dragons to have survived the Elder Dragon War. He styles himself "the mind-ripper, the deathbringer, the winged dark that terrifies your dreams. The first to witness the sun rise on Dominaria, and the last to watch it set for the final time". Mind ripper - hah (mind) vaaz (rip) Death bringer (nok, praan - rest in death) Other key words: viing (wing), vul (dark), maar (terror)

That gives us the following pool of words to choose from: Krein, ul, vith Rah, drog, hah, vaaz, nok, viing, vul, maar I personally think the first two is your best bet for the start of the name, since krein and ul since they describe him and fit all the descriptions. Then choose from one of the other words to finish. Also, remember you can choose the order of their appearance: Krein ul ___, Ul krein ___, ___ ul krein, ___ krein ul.

My personal recommendation is Kreinulvith (Sun-eternal-serpent)