Well for starters, you simply can, but typically there will not be too many replies.
The Facebook commander group is rather good at responding, but typically it is better to ask what cards go well with a commander/build and then supply your color/budget.
Most people won't look at your decklist. It isn't simply because they are lazy (though it is some of that and that they don't want to spend the time looking at what you already have). It is the fact that usually people will just post the decklist and say, "I am trying to build this, help!".
The problem with this approach is that there is no correct way to make the perfect deck and it is highly subjective. The art of building a commander deck is not like trying to draw a horse and then comparing it to a photograph of the best horse at show this year, it is more akin to abstract art. There are all sorts of things that could possibly be going on. Perhaps the person wants to keep running this card be cause the old nice guy at the book shop gave it to him. Perhaps the point is that all the artwork contains stairs. Perhaps Someone is trying to make a Voltron deck with an Azusa, Lost but Seeking. An outsider with limited information is like Clippy from Office 95: we can say "hey it looks like you are trying to do XYZ" but more often than not we are not 100 at the meat of what you are trying to get your deck to do. That is also often an issue with the person creating the deck, they just want the deck to do something well but they are not sure or don't care what, just as long as it somehow wins at their table. Some people want to know the cEDH options. Other people don't want to hear about obvious things like Sol Rings or Command Towers (though some people might not even know about these cards, the responders have no real idea).
This is why I more often than not when I am stuck with a current deck's iteration check what other people have already done.
There are a lot of decks to look at on this site, as well as at Tapped Out and MTGgoldfish, though that pales in comparison to EDREC.
I don't stop there though, I look for build types and what people use for similar commanders, I heavily use Youtube too.
After getting all that, I take everything I found, factor in my budget as well as the cards I already have on hand, and then I make my deck an amalgamation of all the things I liked that I found (and can afford).
It doesn't hurt to know what cards exist out there either. Using Gatherer's advanced search or Scryfall's I can look for key words or phrases for things I want more of in my deck. When I started playing, it was easy to spend a weekend and learn all the cards...there are a lot more out there now, but knowing things exist and watching posts like "card of the day that you might not know about" will keep you in the loop with lesser known tech that can really be a boon.
Lastly spoilers (shown on this site for example) are not just good for playing Standard (I mean honestly it is necessary to know your draft options if you want to stand a chance these days). Knowing what is coming out will tell you what you can add to your deck as well as what you need to worry about/plan for when it is coming at you across the table next month.
That being said, you can always also peruse this forum's archives if you are using an older, more established commander.
So if you are going to post a decklist, don't just post a decklist. Tell us what power level you would like it to be (helps if you tell us what power level you think it is now), whether you want it to be cEDH or not, what you are married to (ex: must it be this commander? must it be this archetype? Is there a theme? Are you telling a story? Must it be by a specific artist or cards from a certain year?), and your budget. What is easiest is if you ask us non-open-ended questions: should I do A or B? I feel like Card X isn't quite working with ______, any suggestions for substitutions? How can I deal with Cyclonic Rift when it is played against my deck?