Since you are trying to print double quotes in a double-quoted string, you need to escape the internal quotes. And to avoid the inverted commas, you also need to avoid backslash escapes. Thus, a literal double quote must be entered as \\\". You can do this a little cleaner by using string interpolation instead of the usual string concatenation.
jq -r ".[] | \"Result is: \\\"\(.a)\\\".\""