equivalent Pantone to a CMYK

If you don't happen to have Photoshop to do what has been correctly suggested several times here, another thing you CAN do is go to Pantone's actual website. They have a tool (under "Find a Pantone Color") where you can punch in your CMYK values and it will offer a handful of suggested matches from whatever set of Pantones you are working with. It's best is to convert to the Solid Coated library, as it's the one with the most vibrant values. 

Then, you can go back to Illustrator and select that swatch from the built in Pantone libraries. However, be warned that the libraries in CC apps are not Pantone's latest, so the Pantone site may suggest a number that is not in your Illustrator's library.

There is no 100% equivalent. Adobe adn pantoen have their own mathes, and those values have chaengs love the years.

After having matched many color by putting a press proffs next to pantone solid coated swatch book, I would say Adobe's match are better than patnone..

I use Photoshop click on the foreground color at bottom of tools, then enter your CMYK values. Then click on color libnraries.

Choose the color system here,

and viola you have a match.

About the safe way.

Pantone colors are used to print (flat) .colors that are not possible with CMYK inks.

There are not Pantone colors for every possible CMYK combination, some are close but different.

So it is a matter of taste.

Make sure your Edit > Color Settings are set correctly for your region printing process.

You can create a CMYK color in Photoshop, and click the Color Picker in the Tools panel.

Select Color Libraries and select the Pantone Library you want.

You can also do it in Illustrator.

Select an object with a CMYK color.

Choose Edit > Edit Colors > Recolor Artwork

Select Color Library and select the Pantone Library you want.

No, there isn't a safe way.

You can let color management do a conversion, but it might not meet your expectations. And it would also depend on properly set up color management.

Pantone also has conversion on their website, but it's not quite clear which color management settings they use (especially for North American needs it might be suffcient, for other areas maybe not).

And then: CMYK ≠ CMYK. You will need to know the exact color space.