Questions & Answers about Я не могу найти свой кошелёк.
Why does the sentence use свой instead of мой?
Свой is a reflexive possessive pronoun that means 'one's own'. In Russian, when the object belongs to the subject of the sentence (in this case, Я), you use свой. While мой isn't strictly wrong here, свой is much more natural and is the standard way to express this.
Is свой кошелёк in the Nominative or Accusative case here?
It is in the Accusative case because it is the direct object of the action (it is what you cannot find). However, because кошелёк is a masculine, inanimate noun (an object, not a living person or animal), its Accusative form looks exactly the same as its Nominative (dictionary) form. The pronoun свой simply changes to match this masculine inanimate form.
Why use найти here instead of искать?
Найти is a perfective verb meaning 'to find', which focuses on the successful result. Искать is an imperfective verb meaning 'to look for' or 'to search', focusing on the process. If you used искать here, the sentence would mean 'I cannot look for my wallet' (perhaps because you do not have time), rather than 'I cannot find it'.
What is the infinitive of the verb могу?
The infinitive is мочь (to be able to / can). It is a highly irregular verb. It uses a 'г' sound for the 'I' and 'they' forms (я могу, они могут) but switches to a 'ж' sound for the others (like ты можешь, он может).