Here is ETIQUETTE VIGNETTE NUMBER SIX – Inspecting Quitted Tricks (refs: Law 66A – C.)

     a. A “quitted card” is a card turned face down after it has played to the current trick.

     b. A “quitted trick” is when all players have played to the current trick and faced their cards down.

     c. “So long as his side has not led or played to the next trick, declarer or either defender may, until he has turned his own card face down on the table, require that all cards just played to the trick be faced”. (Law 66A; carefully read that again.)

    d. “Until his side has led or played to the next trick, declarer or either defender may inspect, but not expose, his own last card played.” (Law 66B)

    e. “Thereafter, until play ceases, the cards of quitted tricks may not be inspected (except at the Director’s specific instructions; for example, if necessary to verify a claim of a revoke.” (Law 66C; emphasis mine)

    f. Notice when “Thereafter” occurs:

       1. “So long as his side has not led or played to the next trick…”

       2. “Until he has turned his own card face down on the table…”

       3. “Until his side has led or played to the next trick…”

       4. “…until play ceases…”

    g. “Can I see that again?” asks declarer or a defender.  Sure, but only before “Thereafter”.

In short: 1) ask to see all the cards played to the last, quitted trick; 2) when your card is unquitted (remaining face up once played to the current trick) and not so on the table; 3) and prior to “thereafter”.