Can a judgment be issued against me without being served?

Maybe. Someone would have to swear he's tried to serve you and been unable to do so because you can't be found or have avoided service, and then do something reasonably calculated to notify you that you've been sued, but it's possible. Occasionally (rarely) a process server will simply lie and say he's served you when he hasn't, but even then it'll be very difficult to get a judge to believe you over the process server. If you know you've been sued, don't try to escape liability by avoiding the process server. It won't work.

It depends but generally, no, a judgement should not be entered unless you have been served. After filing, a petitioner must also file a proof of service showing that you were properly served with the court. If you were not properly served, the judgement entered against you can be overturned.

Technically, no, but practically, yes. You can be deemed to be served by publication and not even know about it. If you were in an accident and think there is a possibility you could be getting sued, report it to your insurance company right away and, if you're not too late, they'll provide you with a lawyer and defense.

No Before judgment enters there has to be proper service of the original complaint and summons.

Generally not, but there may well have been substitute service. See an attorney with the details.

Not in a typical case. The way a suit should proceed is you should be personally served if you are being sued as an individual (service on corporations can be different) within the life of a Summons. You then have a specific period of time within which to file an Answer. The case then becomes at issue and a Judgment would only be entered upon a verdict (jury or judge, depending on what was pleaded). However, there are other ways to enter a Judgment, such as on Motion, because a Court Order isn't followed, etc. Also, if you were unable to be served personally, the other side could have applied to the Court to serve you be alternative means, and if an Order was granted allowing that, then it is possible you were "served" without knowing it and that when you didn't file an Answer, the Court allowed a Default Judgment to be issued. You should check the court where you think there could be a possible Judgment against you to see if one has been filed. If so, you will want to hire counsel to determine if there are any legal grounds to seek relief from same.

No. Actual service or service by publication is necessary. Check out how the Judgment was taken.

Depends upon how service was effected. Some times personal service is required and in some situations personal service is not required.