What is "Nodi Safarta"?
Rashi: You know the number of places I went to flee. Radak - just like You counted my wanderings, guard them with You to take vengeance from my enemies.
Malbim: You counted the number of times I relocated, how many days I was wandering and in how many places.
Why did he ask Hashem to put his tear in His flask?
Rashi: It should be guarded in front of You.
Radak: This is a metaphor - just like it is normal to guard water in a flask, guard my tears. I.e. do not forget them.
Malbim: My tears should be in Your flask and b'Sifrasecha, i.e. in Your calculation. E.g. if it was decreed on me 10 wanderings, and in one of them I had pain and cried like [is proper] in 10, join the number of tears to the calculation of wanderings, to diminish the time of wandering based on the pain and tears.
Why does it say "ha'Lo b'Sifrasecha"?
Rashi: It will be in Your count, to count it with my other afflictions.
Rashi citing Menachem: It is in Your Sefer.
Radak: "Ha'Lo" is to strengthen and make zealous, like "ha'Lo Tzivisicha Chazak ve'Ematz" (Yehoshua 1:9), "ha'Lo Shamat Biti" (Rus 2:8). Sifrasecha is a metaphor, like "va'Yikasev Sefer Zikaron Lefanav" (Mal'achi 3:16). What is written is not forgotten; the Sefer always reminds him.
Malbim: Refers to 56:9:2:3.