Both can mean on the table, but they are used a little differently.
In many everyday contexts, Italians prefer su + article:
So in this sentence, sul tavolo is the most normal choice.
Ancora is an adverb meaning still (or sometimes again, depending on context).
Here it modifies the adjective visibile, so è ancora visibile means is still visible.
This word order is very natural in Italian:
You may sometimes see adverbs in slightly different positions, but in this sentence ancora before visibile is the normal choice.
Yes, it does agree with macchia, but visibile belongs to a class of adjectives that have the same form for masculine and feminine singular.
So:
For the plural, it changes to:
So the agreement is there, but the singular masculine and feminine happen to look the same.
Because sul tavolo means the stain is located on the table.
So:
Italian often uses a prepositional phrase after the noun, just like English does.
Yes, a little.
The original sentence:
is the most neutral and natural version.
You could also say:
This is grammatically possible, but it may sound as if you are focusing more on where it is visible.
So the original order is usually better if sul tavolo simply identifies which stain you mean.
Yes. That would be a natural alternative, but the structure is different.
The original sentence is more descriptive and a bit more formal or neutral.
The si vede version is often more conversational.
A simple pronunciation guide is:
La MAK-kya sul TA-vo-lo eh an-KO-ra vee-ZEE-bee-leh.
A few key points:
Italian pronunciation is usually quite regular, so once you learn the spelling rules, it becomes much easier to read aloud.