If your aunt had a will Nevada law requires that it be filed within 30 days of her death by anyone having possession of it. However, it takes effort and cost $18 to file the will and in actual practice the will is usually only filed if someone needs to begin a probate proceeding. Will filings and probate proceedings are public and can be accessed online. Google Clark County court and eventually you will get to the right website. Keep in mind that probate filings are under the family court heading.
However, many lawyers, myself included, encourage people to plan so that their estate pass outside of the probate process by using trusts or joint accounts or payable on death accounts.
There is no easy answer to your question. If your uncle won't tell you anything, then you can go to the Probate Court to see if a Will has been filed or you may have to have an attorney file an Administration or Intestate proceeding to ask to be appointed to oversee your aunt's estate. That will usually flush out any Will that exists that your uncle has been withholding.
Or you can contact all attorneys nearby where she lived to see if any of them were her attorney.
Speak to a local estate attorney about this matter.
In addition to the good advice that has already been given, I will also let you know that there is a procedure available through the courts to compel someone to disclose a will. I would try to exhaust other remedies first, but this is an alternative if you find yourself without other viable options.