The wh-ever words are used primarily as heads of free relative clauses. When the wh- word is a pronoun (what, who(m), which) these clauses act most often as NPs, and when the wh- word is a proadverb (when, where, how) they occasionally act as NPs.
[SUBJECT NPWhatever she means] is bound to be wrong.
[SUBJECT NPWherever the children are] is the place to look for him.
[SUBJECT NPWhoever told you that] is a very wise woman.
[SUBJECT NPWhenever you want to go] is fine with me.
[SUBJECT NPHowever you did it last time] should work here, too.
So the answer to your basic question is 'Yes'.
However: the particular sentences you give as examples, although syntactically sound, are semantically very unlikely.
Wh-ever words always refer to a set of possible referents, not a single referent; and they give the hearer a ‘free choice’ to select any member of that set as a relevant particular referent. The the -ever piece of the word expresses the speaker's indifference to which member of the set is selected.
But in sentences like I don’t know X or I wonder X or X is unclear, a free relative clause standing for X is distinguished by grammarians as an ‘embedded question’ or ‘interrogative content clause’: the clause implies a question—what?, where?, who?. These sentences express a primary concern with identifying the particular referent. Consequently, the -ever forms are rarely used here, only the bare wh- forms.
I don't know what she means.
I don't know where the children can be.
I don't know who told you that.
I don't know when we're going.
I don't know how to do that.
Note, however, that the -ever forms are often employed as intensifiers (I have no idea whatever), and in conversation you will occasionally encounter this use ‘displaced’ onto the head of a free relative clause. In such cases the -ev- syllable will receive strong emphasis:
I can’t imagine whoEVer she might think she is to carry on like she’s the Queen of England.
But this use is strictly colloquial, and should not be employed in formal contexts.