Selecting attributes from multiple tables via foreign key
Essentially I'm trying to select all from table 2, ...

So we start with Table2 as our basis for the query:
FROM Table2


... but table2.att_1 and table2.att_2 are foreign keys of table1.id.

We'll likely need two (outer) joins to the same table (Table1), one for each foreign key:
FROM Table2
    LEFT JOIN Table1 ..
    LEFT JOIN Table1 ..


What I want to achieve is extract the following:
Value of Table2.ID

SELECT Table2.ID


Table1.Att_1 where Table2.Att_1 = Table1.ID
Table1.Att_1 where Table2.Att_2 = Table1.ID

Right, those verifies that we want 2 left joins and the ON conditions:
SELECT 
    Table1.Att_1
FROM Table2
    LEFT JOIN Table1 ON Table2.Att_1 = Table1.ID 

and
SELECT 
    Table1.Att_1
FROM Table2
    LEFT JOIN Table1 ON Table2.Att_2 = Table1.ID

Oops, we have a problem to combine the two joins. We'll need to alias those tables as we have a table appearing twice and it's good practice nonetheless:
FROM Table2 AS t2
    LEFT JOIN Table1 AS t1a ON t2.Att_1 = t1a.ID 
    LEFT JOIN Table1 AS t1b ON t2.Att_2 = t1b.ID


Value of Table2.Att_3

SELECT t2.Att_3

The whole query becomes (after adding some column aliases as well):
SELECT t2  . ID     AS  ID,
       t1a . Att_1  AS  Att_1_a,
       t1b . Att_1  AS  Att_1_b,
       t2  . Att_3  AS  Att_3
FROM Table2 AS t2
    LEFT JOIN Table1 AS t1a ON t2.Att_1 = t1a.ID 
    LEFT JOIN Table1 AS t1b ON t2.Att_2 = t1b.ID
  ;