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It must be a shorthand way of writing what's in the previous bar: instead of writing all three triplets out, he's written one, with the '3' over it, saying it gets played thrice. As each chord needs to be staccato, he's put three dots over it, to signify each staccato.
This will be a G7b9 chord. Where the 9th is flattened from A to Ab. So, the whole chord has pitches G B D F Ab Although the "-" sign is sometimes used to denote a minor chord (a chord with a minor 3rd), it can also be used to denote a minor, flattened or diminished interval in a chord. For example -5 for b5, or in this case -9 for b9.
As Laurence Payne's comment says, you've encountered one form of musical shorthand. There are a few layers of shorthand here so I'll break it down for you. Stripping the first of the first measure of the second line of any shorthand markings, we have just a dotted eighth note. Now we'll look at that slashy mark across the stem. It just means to subdivide ...
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