A friend gave me what appears to be a slim line, 3" long, older stainless steel pocket knife. ...
The blade is locked in the closed position, and there is no sign of any buttons or other blade releases anywhere on it. The blade does not have a nail groove to open it, and doesn't open with a gently pull of pliers. Any suggestions on how to open the blade would be appreciated. Thanks. Don
Here's something you might try. If it's a liner lock, turn it over and look at the front, where the blade joins at the handles. Look at the groove where the blade rests when closed. There may be a small flat spring that locks the blade into place when it's open.
Other than that, you could have a very stiff spring or froze mechanism.