How to pronounce 'et al' in presentation speech?

The standard English pronunciation can be found in a dictionary, see, e.g., et al. at MacMillan dictionary.

However, during a presentation, instead of reading that abbreviation, it is probably nicer to say something like: "Smith and his/her group/coauthors/colleagues published the paper [...]".

I often just say "and others", "and friends", or just "Foo" for "Foo, et al.". People can see on the screen that there are others and refer to your references to see who those others are. No one is misled or confused if you drop the others in what you say aloud.

Another solution, if there aren't that many authors, is simply to say all names out loud when presenting. In my field, where papers with more than 5 or so authors are uncommon, sometimes we would use "et al." to avoid having to fit more than one or two names on the slide, but the simplest is to say all names out loud when presenting. (And afterwards you can just say "they".)

Of course, this requires sufficient familiarity with the work to know off the top of your head the name of all these authors.