I know that perhaps this is a ridiculous thing to ask, but I'll ask anyway, just to make certain.

The only Ca'Non examples of the verb {ja'} which I know of, come from tkd and they are the following:

{nuja'rup} "they are prepared to tell us"
{qaja'pu' HIqaghQo'} or {HIqaghQo' qaja'pu'} "I told you not to interrupt me"

In these Ca'Non examples the "prefix trick" way of use is employed (I don't know how else to describe it), i.e we don't have {maHvaD ja'rup}, and we don't have {SoHvaD jIja'pu' HIqaghQo'}/{HIqaghQo' SoHvaD jIja'pu'}.

So, the thing I'm wondering is this..

Is it necessary that whenever we use the {ja'} we need to use it the "prefix trick" way? Can't we use it with the {-vaD} way too?

We don't know that the nuja'rup and qaja'pu' examples are using the prefix trick. All we know is that their prefixes agree with the person or people being told something. Taken by themselves, we have no way of knowing whether this entity is considered a direct or indirect object.

But we do have examples of explicit indirect objects with ja':

'ej chaHvaD lut ja'
And told them his tale. (paq'batlh)

We even have unambiguous examples of the prefix action on ja':

DaH naDev jIHtaHbogh meq Saja'
Now I will tell you why I am here. (paq'batlh)

And lest you jump to the conclusion that the object of ja' must be the thing told, we have a counterexample where the people told are the object:

loDnI'Daj vavDaj je ja' qeylIS
Kahless tells his brother and father (paq'batlh)

I believe this all comes down to the definitions of the terms object, direct object, and indirect object. In Klingon, object is a syntactic role, referring generally to the unmarked* argument that precedes the verb. A direct object is a semantic role, referring to a noun phrase or pronoun upon which the subject is performing the verb. An indirect object is a semantic role, referring to a noun phrase or pronoun which receives the result of the verb.

* Unmarked meaning by type 5 noun suffixes not including -'e'.

chaHvaD lut ja' qeylIS Kahless tells them the tale.
The object is lut, because it is the unmarked argument to the verb and precedes it. The direct object is lut, because it is the noun phrase upon which the subject is performing the verb (the tale is being told by Kahless). The indirect object is chaHvaD, because they are receiving the telling of the tale.

loDnI'Daj vavDaj je ja' qeylIS Kahless tells his brother and father.
The object is loDnI'Daj vavDaj je, because it is the unmarked argument to the verb and precedes it. The indirect object is loDnI'Daj vavDaj je, because they receive the telling. There is no direct object, because it is not said what Kahless tells.

DaH naDev jIHtaHbogh meq Saja' Now I will tell you why I am here.
The object is naDev jIHtaHbogh meq, because it is the unmarked argument to the verb and precedes it. The direct object is naDev jIHtaHbogh meq, because it is the noun phrase upon which the subject is performing the verb (it is told by me). There is no indirect object, but one is implied because by the prefix trick the prefix agrees with a second-person, plural object instead of the stated third-person object, so it's understood that the indirect object is tlhIH.

qaja'pu' I told you.
There is no object, because there is no argument preceding the verb. There is no direct object, because nothing is said about what is being told. There is no indirect object, but one is implied by the prefix agreeing with a second-person singular object, so we understand the indirect object to be SoH.

Especially in this last example, it's important to realize that knowing whether an object is a direct object or indirect object is purely a semantic issue — that is, the meaning of the words decide. This is exactly the same between English I told you and I told a tale: you understand that you is an indirect object and a tale is a direct object based purely on your understanding of what the words and sentences mean, not by any analysis of its syntax.

So the answer to your question is, yes, you can say SoHvaD jIja'pu', HIqaghQo' and maHvaD ja'rup. Given the relative lack of this sort of thing, however, I wonder whether it's normal to do so. My impression is, as far as speaking goes anyway, it's quite common for the prefix to agree with the indirect object, whether because the semantic indirect object is the syntactic object or because the indirect object is being implied by the prefix trick.

-- 
SuStel
http://trimboli.name