When your opponent Tribute Summons with your "Zolga" using "Soul Exchange", the controller of "Zolga" increases his Life Points.
When your opponent takes your "Zolga" with "Change of Heart" and Tribute Summons with it, your opponent (the controller of "Zolga" when it was Tributed) increases his Life Points.
When a Tribute Summon using "Zolga" is negated by "Solemn Judgment", you don't increase your Life Points.
The effect of "Zolga" can be chained to, and is Step 1 of a chain after a successful Summon. Effects like "Trap Hole" would be Step 2.
When you Tribute Summon with 2 "Zolgas", both "Zolgas" effects are activated.