The ampersand symbol & means and which in Latin is et. Today we use the abbreviation etc. to mean et cetera which in Latin means and so forth. In the past, English writers used the ampersand in place of the et.
I wonder what it means is a simple declarative sentence.
I wonder, what does it mean? is a question embedded in a sentence. This type of sentence would be appropriate in narrative, or story-telling type writing.