Index -> Appendix -> Skills
If a card affects the "skills" of a character or adversary without specifically naming any of the four skills, it affects only those skills that character or adversary already has.
Part of Bra'tac's game text reads: "
or
: While Bra'tac is ready, each Jaffa support character gets skills +1." Artok is a Jaffa support character who has 2 Combat, and no ratings in any other skill. Bra'tac would give Artok +1 Combat, but no Culture, Science, or Ingenuity.
A rating of 0 is not the same as having no rating; a 0 can be modified by cards that affect "skills."
Seasoned Travelers' game text reads: "Choose a team character to get skills +1 until the end of the current mission for each glyph he has." This card could give 1 Science to Teal'c, who normally has 0 Science.