Your problems are straightforward. In the first instance, you haven't declared the variables properly. Per nwscript.nss:
void RemoveJournalQuestEntry(string szPlotID);
Since the plot ID is a string it must be inside double quotes, like so:
RemoveJournalQuestEntry("tat_IzizCaptive");
Note that this function removes the quest, as stated - i.e. deletes it entirely. Typically you will want to advance a quest to a closed stage, assuming one is available, so that it is still viewable by the player in the completed quests tab. You can do that with:
void AddJournalQuestEntry(string szPlotID, int nState, int bAllowOverrideHigher=FALSE);
Where you state the state number you want. The final TRUE/FALSE variable allows you to override a high numbered plot state (e.g. 90) with a lower number one (i.e. 20) if that is required. Typically it's not needed, but there are a handful of vanilla quests that have low numbered end states. If you are making your own custom quests, as seems to be the case here given the plot ID, then you can avoid that being a problem by using incrementing state numbers with the ending/s using the highest value/s.
If instead you are trying to deal with the vanilla quest, its plot ID is tat17aa_jawarescue (all the quests are found in global.jrl). Also note that quest states can be set directly via a DLG, as is the case here when talking to the Jawa you free in the Sandpeople Enclave.
For the second instance, as the compiler error stated, you have an undeclared variable, oPC. You either need to declare it in your script, like so:
object oPC = GetFirstPC();
Or simply change your existing line to:
GiveXPToCreature(GetFirstPC(), 250);