Borek, forgive me of my ignorance. I have to admit that my chemistry is poor. Thanks for explaining the essential basics. I understand now why strong acids can't be determined by titration.
Two separate things, which you are mixing now - perhaps your thnking is OK, but wording is wrong. You can use acid/base titration to determine AMOUNT of strong acid, you just can't use titration to determine its pKa.
For the latter question, sorry diluting strong acid should raise the pH. By the same principle, is it still not possible to use titration because the strong acid is still fully dissciated?
See above - you can determine amount (although if the concentration is too low titration is of no use). You can't determine pKa, reason (full dissociation) remains the same regardless of the concentration.
Note: reality is a little bit more complicated, but it doesn't change the outcome - you can't use titration for pKa determination for strong acids.