User Defined Symbol Command is missing in NX10.
Solution
1. Start NX10 and create a new part
2. Change to the Drafting Application
3. Go to Menu-Help-Command Finder and search for "User Defined Symbol".
By default this command is currently hidden.
In the Command Finder menu -> MB3 on the "User Defined Symbol" command
4. Add the command to the desired location
Notes and References
Hardware/Software Configuration
Platform: INTEL
OS: windows
OS Version: 764
Product: NX
Application: DRAFTING
Version: V10.0
Function: SYMBOL
Ref: 001-7686065