TL;DR edit: Basically, was he a hustler who got lucky or did he actually know how to do stuff?
For instance, he could certainly teach me some dialects of Italian, Castilian, and Portuguese. He worked in his parents' cheese shop and his brother's cartography shop, so he might know something how to make those things (but maybe not). He was a business agent for some wealthy Genovese families, so presumably he he knew his way around some accounting or management techniques. I have to assume he knew how to ride a horse.
Could he teach me to sail, tie knots, or navigate by the stars? Did he know how to use a sword or musket? Could he cook, treat a wound, repair his boots, construct a shelter? His brother was captured by pirates—did Columbus know anything about naval combat? Or was he more of an entrepreneur who relied mainly on soft skills like salesmanship, and hired people to handle the technical stuff?
Apart from specific biographical details about Columbus himself, what was the typical skillset for someone in his general professional category at the time? How did this differ from the kinds of things that your average Joe in Genoa or Lisbon would be expected to know how to do to get around in day-to-day life?
Christopher Columbus was a very intelligent man, more than reasonably educated thanks to having worked for the Centurioni family as a commercial agent, and while working for them he sailed across the Mediterranean to places like Chios (which was a Genoan posession administered by the Giustiniani family). Under the Centurioni he also navigated the Atlantic to some extent: we know that he at some point made businesses for the Centurioni in Porto Santo, but it did not go as well as expected, and he was sued for it. A notarial transcription by Ventimiglia of the procedure is preserved at the Archivio Nazionale di Genova, a famous document called "Documento Assereto" honouring its discoverer Ugo Assereto.
Columbus also resided in Lisbon, working with his brother as a cartographer (something alleged by Ferdinand Columbus, Bartolomé de las Casas, and Gonzalo Fernández de Oviedo), and he seems to have been more than reasonably good at it. We only have one surviving cartographic testimony of Columbus' craftsmanship, a small cartographic sketch of the northern coast of the island of Hispaniola, preserved by the Fundación Casa de Alba in their palace of Madrid. There has also been argued that the portolan of Valladolid, a portolan chart of the western African coast, was made by Christopher Columbus, at least according to Jesús Varela Marcos and Demetrio Ramos. If the attribution is correct, we can say without a doubt that Columbus was a great mapmaker.
The now famous navigator could have definitely taught you about astronomy and how to sail using the stars as reference, and also the sun. At least according to Gonzalo Fernández de Oviedo, Columbus was who first taught the Spaniards how to sail using the sun and its height, but that may be an exaggeration, as there are quite a number of accredited seafarers (or piraetes) from Andalusia sailing as far as the Azores in order to raid Portuguese ships.
According to Ferdinand Columbus (the Admiral's son), his father had certain combat experience. If we trust Ferdinand, his father commanded the galley Ferrandina in the Catalan civil war, acting under the orders of "king" René of Anjou. Also according to Ferdinand Columbus, his father once fought against a French naval force somewhere off the coast of Portugal, his ship was sunk, and he somehow managed to swim ashore and make his way to Lisbon. Ferdinand Columbus is quite a biased source, alway trying to aggrandise his father, so what he says is not necessarily accurate all the time. There are no records of a Columbus, Colón, or Colombo acting as admiral, or even commanding a galley under the banners of René d'Anjou.
Columbus was also an incredibly sociable guy who managed to turn people to his side and convince them, as proven by how a guy like him, tired, widower, and down on his luck in the South of Spain was capable of being on the Royal Court's payroll within two years, being under the protection of the very powerful Alonso de Quintanilla and Cardinal Pedro González de Mendoza.
The Admiral should also be able to teach you some languages, but take his teachings with a pinch of salt. He definitely knew Portuguese and Latin, also Ligurian dialect, which would have been his mother language, but the Spanish he used was heavily contaminated by a previous learning of Portuguese. We can see this in Columbus' own writings in Spanish. A very famous case of his occasional lack of vocabulary is to be found in his diary of the first journey, where he writes "this place is like an island, but not totally surrounded by water" (and Bartolomé de las Casas kindly annotates "he wanted to mean "peninsula"").
Columbus' skillset was nothing out of the ordinary for a sailor and businessman of his time, but he had a great deal of experience from a young a age as a sailor, learning the skills of the trade "from experience" as Gonzalo Fernández de Oviedo puts it, which is to say with no formal education. As Oviedo writes, "what I have said cannot be learned in Salamanca, Bologna, or Paris, but in the school of the compass, being ordinarily at sea with the quadrant in hand measuring the sun by day, and the stars by night with the astrolabe".
Forgot to add: don't lend any money to that Columbus guy, that money will be gone for good. From Giannotto Berardi's testament we know that Columbus was owing him some 200,000 maravedis, a sum which can be tracked to three years earlier. OK, that's not that much for such a strong sum, but in Columbus' last will we see him finally paying some old debts to people in Genoa: 50 ducats to Paolo de Negro and Lodisio Centurione Scotto (money he owed them since 1478), and some 60 ducats to the heirs of Gerolamo da Porto, father of Gerolamo da Porto, to whom he owed money since 1470). He also owed money to a certain jew in Lisbon who used to live close the gates of the jewish quarter in 1484.