In French, if you want to translate "I don't know what to do." you will not say preferentially "Je ne sais pas ce que je fais." (que" is a relative pronoun) but you say as well "Je ne sais pas quoi faire." and that means as in English "I don't know what I will do.". You'll notice that in this form involving "quoi", the word "ce" is not used; "quoi" is not a relative pronoun but an interrogative pronoun used in an indirect question just as in "I don't know what to do." ("what" is an interrogative pronoun in an indirect question). When the form "Je ne sais pas ce que fais." is used that way, the tense is not "présent" but "présent à valeur de futur proche".
Neverheless, in using this form involving "ce" (added "ce", a demonstrative) you imply a context your locutor is aware of, a context in which what you might do has been discussed, envisaged. Thus, "ce" has the fonction of referring to this thing; in fact you could say "Je ne sais pas la chose que je fais." and the neutral pronoun "ce" is nothing but a systematised way (linguistic systematisation) of referring to something that could be called a thing, a matter, a business and what have you. In English, this idea has been gathered under the word "what", which, in this context, is not an interrogative pronoun in traditional English grammar but a relative pronoun, as in French. By means of such a construction ("ce que") you satisfy to the necessity, in connecting "savoir" to "faire", of providing an object to "savoir" and an antecedent to "quoi".
A second possibility for this form ("Je ne sais pas ce que je fais.") is the case where the tense is decoded as a "présent" and then your English translation is surely "I don't know what I'm doing.". In French "ce" is added because you need an object for the verb "savoir" (as in the first possibility) and as well an antecedent for the relative pronoun (qui, que, quoi, dont). The outcome of this is that there is no stated antecedent for "what" in English; as well, there is no stated referent for the pronoun "ce" in French. In this second case, the antecedent is again to be found in the background that unite the locutor to the person spoken to (for instance, a task the locutor is performing usually but that he can't perform well any more, a recent discussion in which the locutor had mentioned that he/she was slowly becoming mentally ill, …)
In English you say "What I do is my business.", for instance. In French the translation is "Ce que je fais me regarde.". You will perhaps understand better when you find out in the explanations below that in English too you sometimes have to rely on a demonstrative (that); it just happens that in English usually a simplified form is used and that this construction is not often needed.
The forms "CE QUI", "CE QUE", "CE QU'" (mere elision of e), "CE DONT", "CE À QUOI", are sometimes treated as pronouns (ref.) and you might consider this option for the sake of simplification. You can use the following correspondence. However, there might be other forms (supplement or alternatives) as I made up the list given from memory. Nevertheless, in traditional grammar "ce" is a pronoun which has for function "antécédent du pronom relatif « qui », « que », « dont », ou « quoi »"
- ce qui => what
- ce que => what
- ce à quoi => what, that which
- ce dont => what
1.sujet (subject case) : ce qui
- Ce qui me fatigue n'est pas le travail. → What is tiring me is not work.
2.objet (object case) : ce que
- Ce que vous dites est vrai. → What you are saying is true
3."objet indirect « à »" : ce à quoi (penser à, arriver à, contibuer à,… depends on the prep. used with the verb)
Ce à quoi vous pensez est autre chose.
→ (usual) What you are thinking about is something else.
→ That which you are thinking about is something else. (This construction, although it is still found, is not often used.)
Ce à quoi vous êtes arrivé est un succès. → What you've managed to accomplish is a success. (In English, the French "indirect object" becomes an object, therefore you use "what".)
- Ce à quoi vous avez contribué est le progrès dans l'enseignement.
→ (usual) What you have contributed to is progress in teaching.
→ That which you have contibuted to is progress in teaching.
(alternative) That to which you have contributed is progress in teaching.
4."objet indirect « de »" (parler de, se soucier de, traiter de,…depends on the prep. used with the verb)
- Ce dont vous parlez est la foire internationale. → What you are talking about is the international fair.
- Ce dont vous vous souciez c'est (de) vous. → What you care about is yourself.
- Ce dont vous aurez à traiter est la première proposition. → What you'll have to explain is the first proposition.
The Guide of the Perplexed - Volume 1 - Page 67
https://books.google.fr › books 2010
For man has in his nature a love of, and an inclination for, that to which he is habituated.
(A more common alternative) For man has in his nature a love of, and an inclination for what he is habituated to.
C'est ainsi car l'homme, par nature, a un amour et une inclination pour ce à quoi il est habitué.
The Encyclopedia of Philosophy - Page 243
https://books.google.fr › books 2012
One meaning of "universe" is "that to which the observed universe belongs"; another is "that which is characterized by a cosmological model."
Une signification du mot « univers » est « ce à quoi l'univers observable appartient » ; une autre est « ce qui est caractérisé par un modèle cosmologique. ».
Philosophy Classics: Greek and Roman Philosophers (Includes ...
https://books.google.fr › books 1967
Consequently if again he thinks that A belongs to nothing to which C belongs, he thinks that A does not belong to some of that to which B belongs;
En conséquence, si alternativement il pense que A n'appartient à rien de ce qui appartient à C, il pense que A n'appartient pas à quoi que ce soit de ce à quoi appartient B ;