The last day of weekdays [1]
It's Friday today, the day when we need to submit a work summary to our department manager.
After I sent the summary to the manager by email, I browsed English websites, but after some time, I just could not concentrate and could not absorb anything [2]. Maybe it was becasue because I was tired, so I came to Italki for a break.
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[1] Your phrase is correct. However, a native English speaker would use a different phrase: "The last day of the working week."
[2] You are correct, you can omit the second 'could not' and say, "I just could not concentrate and absorb anything."