Re: You know what?

[Kemaweyan]

You want say this phrase? I don't know what I can write. Then it would be

  Oel ke omum futa tsun pamrel sivi.
 

[wm.annis]

You want say this phrase? I don't know what I can write. Then it would be

  Oel ke omum futa tsun pamrel sivi.

We really don't have any good examples from Frommer of indirect questions (which is what this is).  It's one of the bigger questions remaining for him on grammar (including transitivity, animacy and unreal conditions).  For now my process would be, start with the bare question form first:

  Tsun oe pamrel sivi peur? What can I write?

and then pull off the question prenoun: peu > 'u.  Then use that alone as the pivot for an attributive clause: 'u a tsun oe pamrel sivi (tsar)¹.  Then stick that into the main clause with the appropriate case marking:

  Oel ke omum 'ut a tsun oe pamrel sivi (tsar).

I strongly suspect using the contracted fì'u/tsaw a forms would not be used for these, since they have particular uses already which are different.

_____
¹ I use tsar because Frommer has clearly stated (Feb 18) that only subjects and direct objects can be the pivot of a relative clause without requiring a repeated pronoun within the relative clause.  Since the si-construction does not, strictly speaking, have a direct object, it seems that relatives on it need resumption.  I have asked Frommer about this, as part of a big slew of si questions, but no answer has yet arrived.

[Tanri]

Ah, that was smart, but I diden't realy understand that tsar thing   

Basically, we have sentence combined of two clauses - main clause and relative (subordinate) clause.
"Oel ke omum 'ut" - this is the main clause "I don't know the thing"
"a tsun oe pamrel sivi" - this is the relative clause "what i can write", attached by "a" to the noun "thing".

In both of these clauses, we need to refer to one noun - "thing". The main clause is clear and out of the question, there is subject in ergative (or agentive, if this terminology sound better to you) case, verb and object in accusative (patientive) case.

The relative clause "a tsun oe pamrel sivi" is the problem, because we need to refer back to the noun "thing".
Just as in english - "I don't know the thing, what i can write" - in the relative clause, there is the noun "thing" as well, but it is unspoken and taken from the context (..., what thing i can write).
This happens in Na'vi too, but it seems that only for subjects and direct objects (objects in accusative/patientive case):

For example, in this sentence:
"Oel ke omum 'ut a oel tsere'a" - "I don't know the thing what i see" / "I don't know what i see"
we do not need to repeat the noun "thing" in the relative clause, because this noun is in accusative/patientive case in both clauses.

On the contrary, in your sentence, ma Ikranari, the noun cases are different.
In main clause you have "thing" in accusative(patientive) case, but in the relative clause you need to use dative case, because verb based on si cannot take direct object.
According to Frommer's notice, in this condition we cannot simply drop the object from relative clause and leave it unspoken. So we need to explicitly write it, in the appropriate case (dative):
Oel ke omum 'ut a tsun oe pamrel sivi tsar.

[wm.annis]

Uhh... I still don't get it 

I don't know how Norwegian works, but in English, relative clauses work like this...

A relative clause is one of several ways of putting an entire sentence inside another sentence.  In this particular situation, it gives you a way to attach a complex description to one of the nouns already in a simple sentence.  For example.

  A man is walking his dog.  I see a man.  I see a man who is walking his dog.

Notice that "a man" is participating in two separate sentences at the same time in the last example with the relative clause.  It's the direct object of "I see a man" and it's the subject of "(a man) who is walking his dog."  It's this double role of "a man" (called either the "pivot" or the "head noun" in linguistics talk) that is funky.  Let's see another:

  A man is walking a dog.  I see a dog.  I see a dog who a man is walking (him).

This example is more complex, because the pivot, "a dog," is acting as the direct object in both clauses.  I put that "(him)" in there to show where the direct object would normally go.  In English, we don't need to do that.  Syntax alone tells us that the pivot is the direct object in the relative clause.  English, in fact, will allow the pivot of a relative clause be nearly any role in the relative clause.  Most languages are much more restricted about that.

In Na'vi, only when the pivot is either the subject or the direct object of the relative clause can you simply use a with no other help:

  Oel tse'a tutet a yerikit taron "I see the person who is hunting a yerik" (pivot is direct object in main clause, subject of relative clause)
  Oel tse'a yerikit a tutel taron "I see the yerik which the person is hunting" (pivot is direct object of both clauses)

If the pivot is any other case (dative, genitive), or is with an adposition, you must use a pronoun in the relative clause to represent the pivot.  For example, the dative,

  Oel tse'a tutet a Neytiri poru plltxe lit., "I see the person who Neytiri is talking to her."

So, I've given a translation in bad English — we wouldn't normally say "to her" in English.  But in Na'vi, because the pivot is in the dative within the relative clause, we have to refer back to it with a pronoun.