Odd place for it to begin with... Check your Applications folder. If it is not in there, then just reinstall Safari from the system discs that came with the machine (custom install - just the Safari application.)... or, what are you using to post this message? Go to http://www.apple.com/safari/download/ select the appropriate version and install it.

Once installed - or if it is in the applications folder - to get it back to the Dock just drag the original application icon to the Dock. An alias will be made automatically. To get rid of the unlinked Dock item, just drag the "?" from the Dock to the desktop... poof... gone.

Normally, you want to keep Applications in the Applications folder - and use an alias if you want it elsewhere. That said, since it is in the Dock, it is always available... so no need,really, to make an alias...