Liquor license

Where do you live as this will determine the answer to your question.

I will agree, laws vary from country to country, if in the US it will vary from state to state and then from county to county within some states and even some cities will have specific laws.

For example, here in wonderful White County TN, we are a "dry" county, you can not buy most hard drink here in bottle or by the drink, and no establishment can serve drinks. Beer and low content wine is allowed ( walmart lobbied for that and got that passed)

Now you can drive 20 miles across the county line and go to a bar.

If you are going to open any estabishment that serves or allows drinking, you need to see an attorney first, since you will also want to limit your personal liablity in case someone sues you, fines you, or other legal action against the business. Also normally you will need an attorney to work you though all the licence laws. In Atlatna for example, you will have to go to neighborhood planning meetings, where citizens and anti drinking people will drill you on why you need to open the business, this is just to get a business licence to open not counting the liquar licence

I'm in Wisconsin, USA. I don't want to open a bar really, more like a house party with a cover charge to recoup costs. I just want to make sure I can't get in trouble for charging people to get in. The major problem with parties is usually underage drinking, but I would be taking steps to ensure that wasn't occurring and without underage drinking occurring I want to know what the cops might use as an excuse to shut it down.

I think your problem is going to be the "cover charge". The DA may well view this as running a business that serves liquor and therefore needs a licence.
I'm sure your local town/city council can give you the basics on this. After which you need a lawyer.

If a store that you want to buy already has a liquar licence do we have to get a new one ?

If a store that already has a liquar license will we have to buy another?