Dataset query for keys of upper levels

Association @@ (KeyValueMap[# -> {#2, #}&] @ dat) // Normal

<|"a" -> {2, "a"}, "b" -> {"y", "b"}, "c" -> {{2, 3}, "c"}|>

Using MapIndexed:

MapIndexed[{#, #2[[1, 1]]} &, dat] // Normal

(* <|"a" -> {2, "a"}, "b" -> {"y", "b"}, "c" -> {{2, 3}, "c"}|> *)

Another possibility is:

dat[{Keys, {Values,Keys} /* Thread} /* Apply[AssociationThread]] //Normal

<|"a" -> {2, "a"}, "b" -> {"y", "b"}, "c" -> {{2, 3}, "c"}|>

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