TCL VMD TkConsole can be found at Extensions > TkConsole.

Type or copy and paste your TCL commands in the window that has just opened and press enter to run them.
Linux users default VMD instalation path (VMDDIR) is /usr/local/lib/vmd. You can get this directory by running the following command in VMD console or in a TK console:
puts $env(VMDDIR) # 'VMDDIR' here is literal. Do not replace by anything.

Discussion: installation problems (see thread "README before reporting installation problems")
Discussion: README before reporting installation problems