You can find the last App/web portal log in information from the candidates' profile (Candidates >> All Candidates >> eye icon against the candidate).

If candidates remain logged in without any log out, it will show the last time they logged in (eg - candidate logged in 2 days back and hasn't logged out yet, instead of showing the last login as 'Today', it will show their last log in as 'in the last 7 days'). If candidate has logged out of the App completely, it may show them as 'Never logged in' but you'd know that they had logged in before by the presence of their profile picture.