See here: Applying Animations - Spine Runtimes Guide: Queuing
Eg:
spAnimationState state = ...
spAnimationState_setAnimationByName(state, 0, "test", true);
spAnimationState_addAnimationByName(state, 0, "walk", true, 0);
spAnimationState_addAnimationByName(state, 0, "jump", false, 0);