If you activate “Sonic Jammer” during your turn, it lasts until the end of your opponent’s End Phase. If you activate “Sonic Jammer” during your opponent’s turn, it lasts until the end of your End Phase.
If “Skill Drain” is activated after “Sonic Jammer”’s effect has resolved, the effect of “Sonic Jammer” is not negated because “Skill Drain” was not active when “Sonic Jammer” was flipped, activated its effect, and applied its effect.
While “Sonic Jammer”’s effect is applied, your opponent can still use the effects of “Wave Motion Cannon”, or “Black Pendant” when sent to the Graveyard, or Field Spell Cards like “Fusion Gate”.
While “Sonic Jammer”’s effect is applied, your opponent cannot activate “Spiritualism”.