You can use $lines(filename.txt) to see how many lines are in the file. Or $read(filename.txt,$lines(filename.txt)) to read the last line of the file. You can then use $gettok() to get the appropriate group of data.
If you're not familiar with how tokens work the main thing to know is that you can choose what character to use as a separator for the data, it looks like you may want to use commas (,) and double quotes (") which are Ascii characters 44 and 34 respectively.
$remove($gettok($read(filename.txt,$lines(filename.txt)),1,44),") <-- should return the time: 20:09:43
$gettok($read(filename.txt,$lines(filename.txt)),3,44) <-- should give you the date: 9.4.2004
$gettok($gettok($read(filename.txt,$lines(filename.txt)),6,34),1,44) <-- should be the first number (I'm assuming that's the low temp?) 20
$gettok($gettok($read(filename.txt,$lines(filename.txt)),6,34),2,44) <-- should be the other number, 56.
NOTE: "Should", I haven't tested this code, it may require fine tuning.